Friday, 8 December 2017

T-72: Part 2

Due to length constraints, the original T-72 article was split into two parts. This part covers the second half of the article. This is not a new article. You can view the first half here. The bifurcation of the original article was forced by the technical limitations of the Blogger platform; although Blogger does not impose a word limit on each post, it stopped accepting updates on 8.12.2017, after crossing the 88,000-word milestone. Perhaps this is for the best, as this might make the article easier to digest, but you, the reader, should be the judge of that, so please give your feedback in the comments section at the end of this article.

TABLE OF CONTENTS, PART 2




  1. Protection
  2. Common Characteristics
  3. T-72 Ural
  4. Gill Armour
  5. T-72A
  6. Kontakt-1
  7. T-72B
  8. How Does NERA Work?
  9. Kontakt-5

  10. Fuel Tanks as Armour
  11. Smoke Screen
  12. Escape Hatch
  13. NBC Protection
  14. Firefighting
  15. Entrenchment Dozer Blade
  16. Storage

  17. Mobility
  18. Engines
  19. Cooling System
  20. Transmission
  21. Suspension
  22. Water Obstacles
  23. Road Endurance
  24. Driver's Station




PROTECTION



A good indication of a tank's true survivability is its resistance to catastrophic destruction, which can refer to the tendency for a fire to start and the likelihood of that fire spreading and consuming the entire vehicle or the possibility of the ammunition exploding. In this sense, the T-72 stands on equal footing with opponents of the era. But seeing as modern rivals now often include armoured or separated ammunition storage, the T-72 is clearly at a serious disadvantage. Nevertheless, the protection level of the T-72 was remarkably high for its time as a result of its combination of thick armour and low silhouette.

Protection qualities depend greatly on the variant being considered. As the years go on, the protection value markedly increases, reaching its zenith with the T-72B2 variant with the Relikt armour package. We shall examine the protection qualities of all the main variants in detail armour-wise.

The myth of the T-72's inferiority in terms of protection is just that - a myth. Various T-72s have proven their worth in various conflicts when placed under competent command, but the lack of media coverage on the successes tend to skew the view in favour of the image of burning wrecks. To list one incident in Grozny, in the year 2000, a T-72B with the tail number 611 took 3 hits from Fagot anti-tank missiles and 6 hits from RPGs during 3 days of intense fighting and remained in battle with only minor damage. Most of the hits landed on the sides of the tank, with one rocket impacting the lower rear of the hull These are the same types of weapons that an Abrams or a Challenger 2 faced during campaigns in the Middle East, and there are plenty of other cases to be found in the second Chechen war. One only needs to be motivated to search.

A lot can be said about the inherent design issues of the T-72, but one cannot accuse it of being made from inferior steel. As a testament to its quality, an ex-GDR T-72M1 tested in Meppen (details here) withstood 24 hits from a mix of 105mm and 120mm APFSDS and HEAT shells on the turret front without a single fracture or crack. Whether or not the shots defeated the armour is a different matter.



COMMON CHARACTERISTICS


The hull side, hull roof, hull bottom and rear armour of all T-72s are identical, regardless of the variant. The hull side and the turret side are both 80mm thick, but the hull side thickness over the engine is slightly thinner at 70mm. The side armour is more than enough to withstand 20mm armour-piercing ammunition fired from various aircraft, such as the AH-1 Cobra firing the 20x102mm round, or A-1 Skyraider, firing the 20x110mm round. Ad hoc use of M61 Vulcan gattling guns on non-ground attack aircraft such as on the F-4 Phantom would not have yielded any better result.


Drive sprocket area. Note the thickness

This picture shows quite clearly how the upper hull side is thicker than the lower sloped side.

The side armour is thickest at the top half, visibly appearing bulkier (as shown in the picture above) both outside and inside, thinning down to 20mm with a modest slope at the roadwheel region. The upper and lower sides are not the same plate. The upper sides are a single, very long piece of steel, while the lower side is actually the same plate as the belly armour. The belly armour was bent into a tub shape and welded to the upper sides. This probably helped increase the resistance of the hull to the explosions of anti-tank mines under the tracks, as the shape encouraged the deflection of blast waves. This is speculation only, but it is supported by evidence that the Soviets were well aware of the improved mine resistance of the M48 Patton due to its arched hull belly design.

The interior surface of the hull sides is coated in a 20mm layer of anti-radiation lining, which can help absorb spall and other secondary penetrator fragments or even stop residual penetration from lower energy projectiles. This is discussed later in the "Anti-radiation" section below.


The thickness of the side armour can be clearly seen here

It is without a doubt that the sides of the tank were only sufficient for a very limited period of the service life of the T-72. Being only 80mm thick, the side armour plate could offer only a fraction of the protective value of the front armour, and this was not a trifling issue. The number of hits sustained by a tank's sides were statistically significant, as shown by the analyses conducted by Dr. Manfred Held in "Warhead Hit Distribution on Main Battle Tanks in The Gulf". The charts below are from the study.




The sides would have been mostly resistant against 105mm APDS like the L28 and its American derivative at combat ranges within a somewhat reasonable 40 to 50 degree arc, but this narrow arc limits the tank's freedom to maneuver in open spaces. The appearance of 105mm APFSDS rendered the side armour completely inadequate as protection against contemporary anti-tank firepower. 

The hull roof is 20mm thick, the rear armour plate is 40mm thick, and the hull floor is 20mm thick. The hull bottom is only sufficient against explosive charges with a mass of less than 10 kg detonated over the tracks and not directly under the hull. These parts of the hull are most likely constructed from the same steels used in the same locations in the T-54 and T-62; 49 S grade steel for rear armour plate and the hull roof, 43 PSM grade steel for the floor. These grades of steel were first used in the T-54 obr. 1953. The hull bottom is constructed from a single plate of rolled steel, which is then pressed into a complex shape with protruding ribs for the installation of torsion bars and a depressed section to accommodate the driver. Reinforcing nubs were pressed into the plate between every torsion bar rib to improve the stiffness of the floor. The side edges of the plate were bent upward to join with the side hull plate, thus forming a tub shape. All this is only possible with the use of low hardness steels like 43 PSM steel, and it is all but certain that this steel is used in the T-72.




The armour plates used in the side hull and front hull armour of the T-72 is medium hardness steel, most likely 42 SM steel with a hardness of around 340 BHN. The cast turret probably employs MBL-1 armour grade cast steel with a hardness of 270-290 BHN. This grade of steel was first used in the turret of the T-62. The HHS (High-Hardness Steel) employed in the tank is most likely BTK-1Sh with a hardness of 400-450 BHN. The appliqué armour plate used in the 1983 modification of the T-72A is probably BTK-1Sh, but may also be simple medium hardness steel.


The lower glacis is a 80mm plate, sloped at 61 degrees. The properties of the plate are identical to the other welded plates used for the hull, like the side armour plate and the front plate of the upper glacis. Being a traditionally weak area of the tank, the relatively poor armour of the lower glacis is partially counteracted by its small size and low exposure to enemy fire. Furthermore, the presence of the upper glacis armour array partially reduces the height of the weakened zone




At a 61 degree obliquity, the lower glacis is immune from anything short of 105mm APDS, but even so, it provides a certain degree of protection at longer ranges. Although the thickness and sloping is insufficient for the lower glacis to resist L28 or M392 APDS on its own at combat ranges, it is supplemented by the strategically placed integrated dozer blade, which is approximately 1cm thick. The dozer blade is probably made from some high hardness armour grade steel, but it is also possible that it is made from high strength structural steel with a hardness of around 200 BHN, as was common for commercial bulldozers at the time. Having the lower glacis backed by the upper glacis array at the top third of its profile and supplemented by the dozer blade for the other two thirds means that the vulnerability of the area to earlier 105mm APDS is significantly reduced. However, later APDS rounds with more elongated tungsten alloy cores and with tungsten alloy tilting caps would not find this part of the tank to be any challenge at any range.

See the photo below to get a better appreciation of the coverage offered by the dozer blade.




SIDE, REAR TURRET


The entire turret is made of cast steel. The side has a considerable curve to it, exaggerated in the T-72B variant, while the rear of all variants have a distinct beak, which houses the autoloader rammer.


The stub ejector port is also visible here

As mentioned before, the side of the turret is 80mm thick, thinning to around 40mm at the rear. The vertical slope of the turret provides a nominal increase in relative thickness to around 88mm when viewed perpendicularly, but the amount of vertical sloping is very minor as the turret is built with a heavy emphasis on horizontal curves. With a thick layer of anti-radiation lining backing it and with the storage bins - plus cargo - acting as rudimentary spaced armour, the sides are more than enough to withstand any 20mm and 23mm shell at point-blank and any 25mm autocannon shell at typical combat ranges (in the vicinity of 1500m). This is including the 25mm M919 APFSDS shell. However, the armour is not thick enough to reliably resist 30mm, 35mm and 40mm shells. Still, with some extra angling, the side turret would have very good prospects. The rear of the turret, however, is completely hopeless.

The shape of the turret is such that the sides will be completely unreachable by enemy fire from within the frontal 70 degree arc. This means that if you shot at the turret at a relative angle of 35 degrees, you will only be able to hit the strong turret cheeks, never the sides. If the relative angle is increased to 45 degrees, the sides will be visible, but then the relative angle will be so steep (80 degrees) that shaped charge warheads might fail to fuse and all KE projectiles will ricochet. Even if an attacking projectile manages to dig into the armour, the LOS thickness is very formidable at 460mm, which is close to the thickness of the turret cheeks. In other words, the turret of the T-72 is very, very tough nut to crack.


It is interesting to note that although the turret of the T-72 lacks handrails for tank riders like preceding Soviet tanks, the practice of hitching a ride was still occasionally taught and exercised.





URAL


The T-72 Ural was the original T-72, and is the least technologically gifted among its "brothers". Although the hull glacis benefited from a rudimentary tri-layer composite armour array, the turret remained purely steel.


GLACIS


The timeline of the evolution of the hull array is as follows (front to back):

1973: 80mm RHA + 105mm STEF + 20mm RHA

1976: 60mm RHA + 105mm STEF + 50mm RHA

1983: 16mm Appliqué + 60mm RHA + 105mm STEF + 50mm RHA


The original upper glacis armour for the T-72 Ural from 1973 is a composite sandwich consisting of a 105mm "steklotekstolit" (glass textolite) layer sandwiched between an 80mm RHA front plate and a 20mm RHA backing plate. The total thickness is 205mm to the normal. The glacis is angled at 68 degrees, producing a total LOS thickness of 547mm. The source for the 105mm thickness figure of the glass textolite layer is "Kampfpanzer" by noted German armour expert Rolf Hilmes. Two glass textolite plates were pressed together to form the 105mm layer.


The high obliquity of the glacis armour presents a mixture of advantages and disadvantages. The most obvious advantage is that the penetration power of earlier APDS ammunition will be drastically reduced and some HEAT warheads may fail to fuse on impact, but the disadvantage is that long rod penetrators will actually penetrate more armour at higher obliquities up until the critical ricochet angle, which is usually around 85 degrees, but depends on the length to diameter (L:D) ratio of the penetrator. This characteristic of long rod projectiles is confirmed by the Lanz-Odermatt equation, and applies to tungsten alloy, DU alloy and steel rods alike. It is known that the higher penetrative power of long rod penetrators on high obliquity plates is caused by the asymmetry of forces acting on the back of the plate as the penetrator passes through, and the glacis armour of the T-72 suffers accordingly.

One benefit of the heavy slope of the armour is that some warheads may not detonate properly. During the famous Yugo tests, the 90mm M431 HEAT shell with the M509A1 PIBD fuze was demonstrated to have a very high probability of failing to detonate against the 60-degree upper glacis of the target tank (a T-54) when the tank was angled 20 degrees sideways. Although 90mm guns were obsolete against the T-72, the bad news is that the 105mm M456A2 HEAT shell also uses the M509A1 PIBD fuze, so the likelihood of having such a shell detonate on the 68-degree upper glacis of the T-72 in combat conditions is very slim indeed. If a shaped charge succeeds at detonating on the upper glacis, it will be handled by the highly effective composite armour array, so let's take a look at that:


Glass textolite is a material consisting of layered sheets of glass textile bonded by resin and pressed together. Glass textolite is not the same as fiberglass, because glass textolites are manufactured using laminated sheets of glass matting bonded together by resin, whereas fiberglass is manufactured using continuous glass fibers or chopped strands suspended in resin.

A U.S Army technical translation of "Plastmassy v bronetankovoy tekhnike" (Plastics in Armor Materiél) originally published by the USSR Ministry of Defence in 1965 gives us some information on the glass textolite and fiberglass types used in the Soviet Union that would have been used in the armour of the T-64 and T-72. The Eurokompozit website gives a description of the glass textolite used in the T-72. It mentions woven glass roving (rovings are woven bundles of glass fibers) and special phenolic resin film, and the phenolphenolic resin-based glass textolite listed in "Plastmassy v bronetankovoy tekhnike" matches the description exactly, so we can say with great certainty that the density of the glass textile layer is around 1.8 g/cc. Rolled AG-4S phenol resin-based fiberglass from the AG-4 series of fiberglasses matches the description to some degree, but this conflicts with Russian sources that explicitly state that "steklotekstolit" was used. Furthermore, AG-4S uses continuous parallel glass threads, not woven glass rovings as described in the Eurokompozit website. The Eurokompozit website states that website mentions that the glass textolite used in the armour uses a specially modified phenolic resin, so it is not likely that a commercial glass textolite was used.



According to the old NII Stali website from way back in 2003, the efficiency of multi-layered armour against APFSDS ammunition increases as the filler density increases at obliquities of 0 to 40 degrees, but conversely, the efficiency increases as the filler density decreases when the armour is angled at obliquities of 60 degrees and more. The final remark is that the absence of a filler (air gap) leads to a negative result, presumably compared to a monolithic steel plate of the same mass, which is logical because the Lanz-Odermatt formula tells us that the penetration of long rod projectiles increases when the obliquity of the target plate is increased.

The site mentions that high strength steels, titanium, aluminium, ceramics and glass textolite were among the materials studied for the composite filler, and that glass textolite was found to be the optimal filler material. Based on the properties of commercial glass textolites, it is extremely likely that the glass textolite used in the composite sandwich has a density of 1.3-1.5 g/cc, and as the NII Stali website stated: the efficiency of composite armour increases when lower density fillers are used at an angle at 60 degrees or more.




These claims also appear to hold true for shaped charge threats as well, as shown in "Jet Penetration into Low Density Targets". One of the simulations detailed in the paper was for a case where a 100mm plate of variable density was placed in front of a filler of variable density. It was found that the velocity of the shaped charge jet tip emerging from the 100mm plate tended to be lower as the filler density decreased, but the jet increased in velocity when the density of the 100mm plate itself was decreased. As you can see from the graph below, the most serious reduction in jet tip velocity occurs when low density material is placed behind a 100mm plate with high areal density (m=500 km/m^2).




The paper goes on to detail that low density materials are more effective against particulated jets than continuous jets. The graph above was plotted with the assumption that the jet emerging from the 100mm front plate is continuous, but the mass efficiency of a filler increases as the density of the filler decreases if the jet is particulated as it enters the filler.





The most optimal configuration is to have a front plate of high areal density in front of a filler of low areal density. This ensures that the jet is particulated as it emerges from the front plate, so that the low density filler performs at an optimum level. Having a 80mm front plate sloped at 68 degrees for a LOS thickness of 213.6mm, the armour of the T-72 Ural should be more than enough to particulate any shaped charge jet from the era, yielding very high efficiency from the glass textolite filler.

The addition of the 20mm steel back plate behind the glass textolite filler was most likely meant as a final barrier against KE threats rather than shaped charges, although a steel back plate would certainly be effective at stopping residual jet particles. The path taken by Russian engineers to reach this solution is detailed by Andrei Tarasenko in his article on the armour of the T-64, where he also describes the armour of its predecessor - the Object. 432. The armour of the Object. 432 had the 80mm steel front plate, but had a 140mm low density filler of glass textolite behind the plate. From what we have learned so far, this configuration would be highly optimal against shaped charges. According to Tarasenko, this configuration was estimated to provide protection equal to 450mm of RHA against shaped charges. However, this configuration was changed to the familiar 80-105-20 combination in the Obj. 432SB-2 variant.





The new 80-105-20 configuration substituted 35mm of low density filler for a 20mm plate. If we look at this design solution from the perspective of mass efficiency against shaped charges, then the mass efficiency of the armour decreased, because 20mm of steel is obviously much heavier than 35mm of glass textolite. However, the level of protection offered by the new configuration against shaped charges did not change; it was still equal to 450mm of RHA steel, as shown by the table below (row: T-64A, column: "KC").


(Note the given areal density figures; 785 kg/sq.m for the T-62, 980 kg/sq.m for the T-64A)

Therefore, the substitution of 35mm of glass textolite for 20mm of steel can only be to improve protection against APDS and APFSDS threats, while maintaining the same level of protection from shaped charge threats.


Regarding APDS threats - the heavily sloped array should be quite adept at defeating contemporary APDS projectiles, which were still credible threats even while new APFSDS was being developed on the other side of the Iron Curtain. The primary threat was the Chieftain, which relied on the powerful L15 series of APDS shells, but 105mm APDS was still in widespread usage as well, though 105mm APDS had virtually no chance of defeating the upper glacis armour.

Part of the function of the heavy front plate is obviously to erode the penetrator, but the reason why a thick plate was placed at the front of the array and a thin plate at the back was in order to effectively break up APDS and APFSDS projectiles. Being fragmented will severely reduce the penetration power of the projectile, partially because the shape of the fragments is not optimal for penetration and partially because the kinetic energy of the projectile is dissipated over a large area for the glass textolite interlayer to absorb. This arrangement is different from simple spaced armour arrangements, which typically consist of a thin hard steel plate in front of a thicker but softer base armour plate. The use of a thicker front plate in the T-72 upper glacis array is probably because the interlayer material plays a much larger role in stopping the projectile than the air gap in simple spaced armour. Residual fragments are stopped by the 20mm RHA backing plate.


It is known that APDS projectiles with a tungsten carbide core break up more readily during their travel through a target plate than long rod or composite APFSDS shells (like the M735) due to the brittleness of tungsten carbide, but some APDS shells do not use tungsten carbide. The L15A3 is a good example of a more sophisticated APDS shell, as it has a tungsten alloy core with a relatively high elongation. The shell has very good performance on highly sloped armour plate thanks to this, but still exhibits the same propensity to disintegrate inside the armour plate as it penetrates, as demonstrated in the picture below (full page originally shared on tankandafvnews). It is not the best example, of course, because the thickness of the defeated plate shown in the picture was at the limit of the capabilities of the shell at that range and at that angle, but the same concept applies: the asymmetry of forces acting on the plate due to the different relative thickness of metal above and below the penetrator cause the part of the plate below the penetrator to buckle, resulting in the early structural failure of the plate compared to a vertical plate. Conversely, the penetrator also experiences asymmetrical forces as it penetrates the plate, causing the penetrator to fracture inside the plate and break apart as it exits. If the target is monolithic, this effect is beneficial as it increases the post-penetration lethality of the shell. Against oblique spaced armour, however, the shell will usually successfully perforate the spaced front plate, but the shattered core may fail to defeat the back plate. The composite armour of the T-72 Ural would be the most difficult target of all.




The graph on the left shows that the penetration of the APDS shell at 1000 yards (914 m) on a steel target at a 68 degree obliquity is between 110mm and 120mm, so the 80mm front plate of the upper glacis array is completely insufficient on its own at that range, but it is thick enough that the tungsten alloy core is shattered as it exits, as shown by the photo below.




Page 3 of the brochure states that the shell is "the first high velocity shot of its type which effectively defeats multiple targets" (armour plates), hinting that it was different from previous APDS designs and that previous designs would have performed worse against spaced armour or perhaps even composite armour. This is most likely referring to the use of a tungsten alloy core as opposed to a tungsten carbide one, as older APDS shells like the L28 have all the other features of the L15, including the shape of the core and armour piercing cap. It is understood that the L15 was the first to have a tungsten alloy core, and that the 105mm L7 received an analogue later on in the form of the L52, which was fundamentally the same as the L15A3 but smaller. The diagram below shows the L15A5, which is structurally similar to the L15A3 and differs only in the alloy of the core. Note the sharp-tipped conical steel armoured cap, labelled "nose pad", on top of the hemispherical nose of the tungsten carbide core.




Despite all this, it is still very unlikely that it could have defeated the upper glacis array of the T-72 Ural even at the short range of 1000 yards, due to the combination of the high slope, high thickness of the nonmetallic filler and the thickness of the front plate. The 80mm front plate should be more than enough to completely erode the tungsten cap, erode most of the core and fracture it as it exits the plate, where it is absorbed by the glass textolite layer and finally stopped by the 20mm backing plate.


In 1976, a new glacis array was introduced for the T-72 Ural-1 modernization. The new array retained the 105mm glass textolite filler, but it now had a 60mm RHA front plate and a 50mm backing plate instead. The total thickness becomes 574mm when angled. The vast majority of the Red Army's T-72 tanks incorporated this newer armour scheme, and this is instantly obvious when we examine the production record of the T-72; the production volume at Nizhny Tagil in 1976 was 1017 units, whereas only 950 units were released during the entire production run of the original model T-72 Ural from 1973 to 1975.


The replacement of the 20mm backing plate in the 1973 variant might be for two possible reasons; a tendency to buckle or bulge excessively when impacted by the remnants of an APDS or APFSDS shell, and possibly its inability to reliably absorb the degraded penetrator of the latest long rod APFSDS projectiles. It is possible that the front steel plate was made slightly harder to further improve its protective characteristics, and because it is thinner and therefore easier to harden further.

A 60mm plate will not be as effective as an 80mm plate at particulating a shaped charge jet, so a more continuous jet will penetrate the glass textolite filler. The glass textolite filler is less optimal against a continuous jet, and it is apparent that not only was the thicker 50mm back plate intended to absorb the rest of the jet, but an additional 10mm of steel had to be added to the array, giving it 110mm of steel instead of just 100mm as in the previous configuration. We can view this as a compromise to improve protection against KE threats while keeping the protection against SC threats at the same level, with the penalty of a reduction in mass efficiency. Therefore, the additional 10mm of steel should not be regarded as additional armour against shaped charges, but as compensation for the reduced front plate thickness. Any attempts to add 27mm of armour (10mm / cos 68°) to the 450mm RHA figure is fundamentally invalid; the protection offered by the 60-105-50 array should still be equal to around 450mm RHA against shaped charges.


Blast attenuation is an aspect often overlooked when referring to tank armour. This is no different for the T-72 Ural, which has an advantage through its laminated hull armour. By placing two materials of drastically different properties in the path of the blast wave, the laminate array's effectiveness in attenuating the blast is significantly improved as compared to homogeneous materials of the same weight. This was quite important seeing as HESH (High-Explosive Squash Head) shells were and still are a British favourite.


In 1983, an additional 16mm plate was added on, which came about as a result of live fire testing of captured Israeli M111 tungsten-cored shells from Lebanon (in the 1982 war in Lebanon). Contrary to popular belief, the Israelis did NOT "discover" that their M111 Hetz could perforate the T-72 from the front "at about 650 meters". The Israelis never got their hands on an intact T-72, nor did they ever face them with 105mm guns in combat. Strong evidence has indicated that at best, the T-72s were destroyed in an ambush by TOW missiles fired at their flanks from gunships.




However, it is true that the M111 "Hetz" was acquired by the Soviet Union. A very popular theory is that these rounds came with the captured Israeli M48A3 that was until recently on display in Kubinka. The M48A3 doesn't have a 105mm gun, of course, but Israelis had a habit of upgrading their tanks. So knowing that the Soviets did capture M111 Hetz in some quantities, then evidently the hull upper glacis of the T-72 (as well as other autoloading T-tanks) was vulnerable to these new acquisitions, thus necessitating the installation of the appliqué plate. As the appliqué plate is only 16mm thick, the boost in armour protection is really quite minor. It is known that the Soviet revelation prompted the application of appliqué armour on the T-64 and T-80 as well, but both received 20mm plates rather than 16mm plates. The reason for this is not that the T-64 and T-80 were more valuable than the T-72 and deserved better armour. Rather, it was because the vast majority of T-72 tanks at the time had already upgraded to the 60-105-50 hull glacis armour scheme while the T-64A and T-64B were still reliant on the older 80-105-20 armour scheme. As it had the newer armour scheme, the T-80B received a 16mm appliqué armour plate in 1983 like the T-72, whereas the T-80 received a 20mm plate in 1979 as part of an unrelated modernization effort to increase its protection to the same level as the T-80B.

Therefore, we can assume that the hull glacis with the 16mm appliqué plate is proofed against the M111 "Hetz" at a range of 500 m, which is in line with the original requirement of the T-72 to be immune from enemy KE ammunition at a distance of around 500 meters. This tells us that the armour must be equivalent to at least 400mm RHA for the plain 60-105-50 hull armour. With the addition of the 16mm plate, the armour should be equivalent to more than 400mm RHA.


The November issue of the famous Russian Tekhnika i Vooruzhenie 2006 (Журнал Техника и Вооружение) magazine mentions in page 14 that in 1993, a report published in the specialized magazine "German Airspace" by A. Mann states that the armour protection of the T-72M1 exhibited protection equivalent to 420-480mm of rolled homogeneous armour when tested against modern 105mm and 120mm ammunition from West Germany. The upper glacis armour of the T-72M1 is the same as the 1976 modification of the T-72 Ural, plus the 16mm appliqué armour plate (16-60-105-50). For all intents and purposes, this can be interpreted to mean that the hull armour is equivalent to 420mm RHA against modern long rod tungsten alloy ammunition like the 105mm DM33 (standard 105mm APFSDS in the late 80's and the decade after), while the turret is equivalent to around 480mm RHA, probably at the cheeks.

It is worth noting that M111 "Hetz" and the similar DM23 were the most advanced 105mm APFSDS rounds of the early 80's, were the best anti-tank ammunition available for the Leopard 1A4 and 1A5 and were practically standard for the remainder of the decade.




High hardness steel is best used as appliqué armour, as in the T-72's case. The hardness and thickness yields the best results for defeating KE projectiles, especially at a high angle, but very high hardness steel is difficult to weld, so it is more than likely that the appliqué plate has a hardness of around 400 BHN, but no more. However, we must keep in mind that this was merely a temporary stopgap measure to keep the Red Army's large fleet of T-72 Ural and T-72A tanks viable against the most common threat - 105mm guns - for the next few years, while the emerging threat of 120mm guns required a serious upgrade in armour protection that took the form of the T-72B.


TURRET




The turret is made from MBL-1 armour-grade cast steel, assembled from two pieces. The turret front, sides and rear are cast as a single piece, but the roof is cast separately and welded on. This slightly degrades the structural integrity of the roof, as the weld seams can be weak points.

According to a well known CIA analysis of a diagram from a captured Soviet T-72 manual, the thickness of the turret at the mantlet area is 350mm. The mantlet is the area immediately next to the cannon. The machine gun port, barely a few centimeters away from the cannon, is already 475mm thick, and from there, the turret only gets thicker, so even the weakest part of the turret can survive a hit from 105mm M392A2 APDS. The diagram is shown below.




The area immediately next to the gun barrel is especially weak due to the gun trunnion. The diagram processed by the CIA is reproduced rather poorly, so an original diagram from a higher quality Soviet T-72A manual gives us a better idea of the armour profile. The trunnion is highlighted below:




Combining the cast steel from the turret with the gun trunnion, the total thickness amounts to only 320mm. While it is definitely quite robust, the strength of the gun trunnion may not be on the same level as the armour-grade cast steel surrounding it. The difference is not likely to be very big, but it is probably big enough to have some meaning for ammunition with a very small margin of penetration, such as L28 APDS rounds. Adjusted for the lower effectiveness of cast steel, this part of the turret is worth between 280mm to 290mm of RHA steel.

The diagram appears to show that only the turret cheek on the right has a thickness of 475mm, and the turret cheek on the left appears to be substantially thinner, but both cheeks are equally thick. Both sides of the turret are symmetrical, and the gunsight interface port constitutes a weak point on the left side of the mantlet, mirroring the machine gun port.




The turret roof over the crew positions are 45mm thick and sloped at 78 degrees, and the thickness of the roof above the gun breech is more than twice as thick, angled at between 78 to 80 degrees. Adjusted for the lower hardness and strength of cast steel, the roof armour is still more than capable of consistently causing all contemporary APDS and APFSDS rounds to ricochet harmlessly. Even depleted uranium long rod monobloc projectiles like the M774 from 1979 would not be up to the task as it had a low aspect ratio (L:D) of 13.32, an ogived tip, and a relatively low velocity of 1508 m/s at the muzzle. When newer and longer long rod penetrators began to appear in the mid-80's, the invulnerability of the roof was seriously challenged.


Due to the geometry of the turret, the maximum physical thickness of the cheeks of around 475mm is not replicated anywhere other than the area immediately beside the gun mantlet. The cheeks become progressively thinner as it nears the edge of the frontal profile of the turret, but the relative thickness increases due to the round shape of the cheeks. From a side angle, however, the relative thickness of the cheeks is significantly lower than 475mm, although still extremely formidable. According to Baryatinsky, the relative thickness of the turret cheeks at a side angle of 30 degrees is 400 to 410mm with a vertical slope of 10 to 25 degrees, noting that other data indicates that the side angle for that figure is 35 degrees. However, the usual format used by the Soviet authorities to express armour thickness is at a 30-degree side angle, so it is more likely to be 30 degrees than 35 degrees. The thickness of the side armour of the turret varies between 395mm to 440mm at a side angle of 20 to 25 degrees.



PROTECTION ESTIMATE


Converting from the physical thickness of the turret cheek at 30 degrees to its equivalent thickness in RHA steel - not neglecting to include the 10 to 25 degrees of vertical slope - the turret should be worth around 385mm of steel.

The physical thickness of the same part of the turret can be determined by dividing 400-410mm by the cosine of 30 degrees, giving us around 473mm; almost exactly identical to the thickness of the start of the turret cheek as determined by the CIA. Based on this, we can be justified in assuming that the turret cheeks of the T-72 Ural offer a generally uniform physical thickness of steel of 505mm, which is worth 455mm RHA when converted from cast steel.


The lack of a composite filling in the turret is disadvantageous when it has to deal with HEAT and HESH ammunition, but this is compensated by the extreme thickness of the steel. HESH works well on homogeneous plate, but there is a limit to how thick the plate can be. As far as the Ural is concerned, HESH is no more deadly than any other high explosive round, which is to say that the Ural turret is completely immune. A bigger challenge would be 105mm HEAT shells. The most common 105mm HEAT round of the day, the M456A2, could only penetrate 425mm of steel armour, which is not enough to go through the turret in a head-on attack, but may have a chance on a shot from the side at an angle of more than 30 to 35 degrees. The fuze on the M456A2 will not work on the roof of the turret due to the extreme slope. Despite the lack of composite armour, the chances of defeating the turret armour from the frontal arc with 105mm HEAT was very, very slim indeed.




GILL ARMOUR



In addition to solid armour protection elements, the T-72 Ural is also equipped with four flip-out panels, known as "gill" armour. "Gill" armour was notoriously fragile. These panels took the place of traditional side skirts and were originally found on the T-64A and were carried over. Why they never made the effort to combine both side skirts and gill armour on standard production model tanks is not known.




The purpose of these panels were to detonate shaped charge warheads at a great distance from the sides of the tank, thus providing a great deal of spaced armour. However, the coverage offered by these "gills" was limited, as gaps will begin to appear past 35 degrees obliquity. Though they could still work at greater angles, the chance of intercepting an incoming warhead becomes slimmer and slimmer. From frontal angles, "gill" armour augmented the high resistance of the T-72 to even the most powerful ATGMs of the time. Even when folded, the panels still provide a modicum of spaced armour, as you can see in the second B&W photo below. It is interesting to note that the suspension is rather densely packed, so there is hardly any room for a shaped charge jet to slip through without colliding with some part of a track or a roadwheel or something. As long as the jet does not break a track link, all that can act as additional armour - especially the roadwheels.






The panels are made of hard vulcanized rubber flaps mounted on sheet steel. They offer absolutely no protection whatsoever from KE projectiles, though it is very clear that there was a lot of missed potential here. The panels are probably great for drying clothes.

The primary disadvantage to gill armour is that the gills are very easy to knock off when maneuvering in wooded areas. The gills are spring loaded, so they bend quite easily if they happen to cross paths with a tree, and the heavy duty hinges upon which the gills rotate are very robust. However, the heavy duty hinges are secured onto the fragile miniskirt with only two small bolts, as you can see in the photo below:


Notice the thick L-shaped wire; it's the spring that flips these panels out.


Struck squarely in the center of any one of the panels from a 30 degree angle, "gill" armour can provide 2.2 meters of space from the hull side armour, more if the panel is struck at the outer edge and less if struck at the inner edge. Under such optimum conditions, a great deal of spaced protection can be achieved. This would have given the T-72 Ural a great amount of protection from guided missiles and man-portable rockets of the era within a 70 degree frontal arc. For example, the diagram below shows the depth of penetration of a 100mm shaped charge increasing to 700mm (7 CD) when the standoff distance is increased to 0.6 meters, but the penetration drops down to less than 400mm at a standoff of 1.2 meters, less than 200mm at 2.4 meters, and less than 50mm at 4.8 meters.




The normal achievable penetration of the 100mm diameter warhead would probably correspond to the penetration at a 15cm standoff distance or less, since the typical built-in standoff for a rocket-delivered shaped charge warhead with a regular pointed aerodynamic fairing without a standoff probe or a spike tip is only around 2 CD or slightly more. As you can see in the chart, an additional 0.45 meters of space in front of the built-in standoff yields the best penetration obtained from the warhead, and this really helps to communicate the peculiarities of shaped charges. Spaced armour can be effective, but only when applied properly and in sufficient portions. For example, if an APC with a ~400mm-wide track had a sideskirt installed to cover the suspension, it would actually become even more vulnerable to a shaped charge grenade. Even at 30 degrees, the sideskirts of a typical tank would not provide sufficient spacing to defeat a tank-fired HEAT shell. Because of this, the primary reason why tanks have sideskirts is to reduce the amount of dust kicked up into the air, mainly to prevent the enemy from spotting the tank from faraway distances and also to improve the visibility for other tanks at the back of a convoy.

Older missiles like the SS.11 (1956) using older shaped charge technology form less cohesive cumulative jets due to imperfections in the manufacturing of the shaped charge liner, so the shaped charge jet dissipates more quickly over spaces. A large but old large diameter missile like SS.11 will most likely fail to perforate the side armour of the T-72 despite having a 165mm diameter warhead with up to 600mm of penetration, whereas the smaller 135mm diameter warhead of the Konkurs missile (1974) might get through, despite having the same 600mm of penetration.

If a "gill" armour panel was struck at 30 degree angle by the warhead described in the diagram, there is a good chance that it could have offered just enough space to protect the 160mm side armour (80mm at 60 degrees). Protection would be guaranteed at angles steeper than 30 degrees since the amount of air space provided would increase drastically, but at such angles, the possibility of striking the thinner (70mm) engine compartment side armour arises. All taken together, the side aspect of the tank is quite evenly protected.


Gill armour is useless from the side

These panels are no longer seen even on unmodernized T-72 Urals, having being rapidly replaced with conventional side skirts as seen on the T-72A. This could be due to two reasons already mentioned above; fragility and incomplete coverage. One concrete advantage of the conventional side skirts is that it keeps the amount of dust kicked up by the tracks under control, but why not combine the two?




Such a modification appears to only exist on Czech T-72M1 tanks, but even then, it is not a standard modification for Czech derivatives of the T-72 or even a large scale one-off modification for the T-72M1 specifically. It is rather likely that the gills simply kept falling off and it became tedious to replace them after every exercise, so they were removed once and for all.




T-72A



Protection-wise, the production model T-72A differs from the T-72 Ural and Ural-1 mainly by the implementation of composite armour in the turret. The gill armour had also been replaced with conventional side skirts. The front hull armour was the same as in the Ural-1. The T-72A can be directly compared to the Leopard 2A0, as both were introduced in 1979.


Glacis Array



The upper glacis armour on the T-72A was identical to the T-72 Ural-1, which was introduced just three years prior. In 1983, the T-72A received a 16mm appliqué armour plate alongside its predecessors. The total thickness of the glacis with the appliqué armour plate now becomes 231mm, or 616mm when angled at 68 degrees. As we have already examined the armour in full detail, there is nothing else to talk about.


Determining the presence of appliqué armour is simple business. The tow hook area is a good indicator. If the cut-out over the tow hook is present, then appliqué armour is present. This is a good way of distinguishing earlier T-72 models from the T-72B, which has thicker armour but no appliqué armour, as sometimes claimed.





"KVARTZ" TURRET

  
Notice the characteristic ledge on the middle of the turret cheek

It should be noted that the T-72A was not the first T-72 model to feature the composite armour turret, which is colloquially referred to as the "Kvartz" turret. The T-72 began to receive the "Kvartz" turret from 1977 onward, which would mean that virtually all of these turrets went to the T-72 Ural-1 model, as the production life of the Ural-1 was from 1976 to 1979. This relatively small batch of turrets had composite armour, but also had the extension for the second optic for the TPD-2-49 optical coincidence rangefinder.




The T-72A had this turret upon its introduction in 1979, and continued to be manufactured with this turret for five more years until 1984. The composite turret features a cast armour cavity on each cheek filled with a material known as "Kvartz", sometimes referred to as "sandbar armour" or "sand rods". "Kvartz" translates to "Quartz", so quartz is probably an ingredient, but the exact composition of this compound is unknown, though the name implies that it includes granules or powdered substances. Based on an ARMOR article penned by James Warford, the armour of captured Iraqi T-72M1 tanks was thoroughly analyzed in the U.S but the composition of the filler has not yet been disclosed to the public. Warford emphasizes that typical sand is probably not used, and he speculates that the name "Kvartz" hints that quartz may be used and recalls the use of quartz gravel as an ingredient in HCR2 add-on armour kits during WWII. The full ARMOR article can be read here.




The three-layer arrangement of the armour may help it attain greater standards of protection than homogeneous armour of the same mass against shaped charges. As noted with the hull array, the composite nature of the T-72A's turret should give it an added damping effect against high explosives and high explosive squash heads, but also against the shockwave of nuclear explosions.


The thickness of the T-72A is unclear, but we can use the same method employed by the CIA to determine the thickness of the turret of the T-72 Ural.



As mentioned before regarding the turret of the T-72 Ural, the CIA determined the thickness of the turret by scaling it against the known length of the barrel of the co-axial machine gun. Comparing the diagram used by the CIA and the diagram from the T-72A manual, we can clearly see that the "Kvartz" turret is thicker. Taking the machine gun barrel to be 680mm long, we find that the thickness of the cast around the machine gun barrel is 370mm - just slightly thicker than on the T-72 Ural. The beginning of the turret cheek to the immediate right of the co-axial machine gun measures approximately 514mm, which is 8.2% thicker than on the Ural turret.




The turret measures 514mm at the start of the cheek, increasing to 600mm at the area directly in front of the commander's cupola. This is all pure cast steel, as the drawing shows that there is no filler at this part of the turret. However, this gargantuan thickness of steel is not sustained for long, as the turret cheek is filled with "Kvartz" for the majority of its profile, beginning from somewhere near the gunner's sight housing, as shown in the photo below. The subject of the photo is the turret of an ex-GDR T-72M1, purchased by Sweden in the early 90's and used for testing purposes.

Looking closely at the photo below, you will also notice that the filler material is clearly not sand. It has a metallic silver colour, and it appears to have some structural integrity, as it has not poured out.




Based on the thickness of the steel and "Kvartz" in the photo, it can be surmised that the cavity containing the "Kvartz" layer, whatever it is, is present in a 1:5 ratio to the steel aspect of the turret, as you can see in the photo below. If we take the total thickness to be approximately 600mm, then the thickness of the cheek at a 30-degree side angle should be 520mm. The outer wall of the cavity should be 208mm thick, and the inner wall should be have the same thickness. The cavity containing the "Kvartz" filler should be 104mm thick, assuming that it is about half the thickness of the outer wall. This is very different from the distribution of thicknesses in the turret of the T-64A, which had almost the same thickness of filler as the steel walls of the composite armour cavity. The low thickness of the filler in the T-72A turret indicates that it has low mass efficiency (ME) but high thickness efficiency (TE) against shaped charges, as the bulk of the work is done by the steel components of the armour.

Coincidentally, this estimation is very close to the estimation done by Militarysta, a forum member of forums such as the Polish militarium.net. However, his thickness estimation appears to be for the turret cheek at 0 degrees, but it should be for 30 degrees. The estimate for "500mm RHA vs APFSDS" is a typo and refers to HEAT, not APFSDS. The estimate done by Militarysta would mean that the T-72A has the exact same protection against KE threats as the T-72 Ural turret, if not slightly less. Needless to say, that is highly unlikely.


PROTECTION ESTIMATE


If the thickness of the cheek in front of the gunner's sight housing is 600mm at 0 degrees, then there should be 480mm of steel and 120mm of "Kvartz", based on the 1:5 distribution of thicknesses of the composite sandwich. But that's not all; we should not forget that the turret is sloped by 10 to 25 degrees on the vertical plane. This meager slope is enough to boost the average LOS thickness of the turret cheek to around 638mm (more or less), making the steel part around 500mm thick and the "Kvartz" layer around 127mm thick. Adjusted for the lower effectiveness of cast steel, the steel component of the turret should be worth around 460mm of RHA steel. The "Kvartz" layer probably has little effect on KE threats, but it should still have some contribution, so a reasonable estimate of the worth of the composite armour as a whole should be around 480mm RHA. This is an improvement of only 5.5% over the T-72 Ural, but the improvement in protection against shaped charges is probably more substantial, likely to the tune of 500 to 550mm RHA. Sergey Suvorov gives a more generous - and more optimistic, I daresay - figure of 500mm against KE threats and 560mm against shaped charges in his article "T-72: Yesterday, Today, Tomorrow", published in the July 2004 issue of "Техника и Вооружение" magazine.

At a 30-degree side angle, the thickness of the cheek in front of the gunner's sight housing would be 520mm, of which 415mm is steel and 104mm is "Kvartz". In terms of physical steel thickness, this is only 5mm more than the T-72 Ural, but with an additional layer of filler. Without neglecting the 10 to 25 degrees of vertical slope, the protection level of the turret at this angle should be equivalent to around 405mm RHA. This is an improvement of only 5.2% over the T-72 Ural, but again, the increase in protection against shaped charges is probably bigger, perhaps up to 450mm RHA.

Compared to the turret armour of a Leopard 2A0, the armour is substantially thinner, but much denser, and much more effective against KE threats. The spaced NERA armour in the Leopard 2A0 should easily make it much more efficient against shaped charges, although the T-72A is not that far behind. This gap was virtually eliminated with the introduction of Kontakt-1 reactive armour some years later.


Circular markings are visible in the photo below. These are filler plugs. Evidently, "Kvartz" is poured into the armour cavity after the cheeks are cast. This is a good foundation to rule out sand as the filler substance, as there would be no need to pour sand into the cavity because sand is used in chill casting molds and it would not be necessary to remove the sand used in the casting process. If "Kvartz" is not sand, then it is quite likely to be a plastic.  




Whatever it is, it is proven to be effective against 3BM-15 APFSDS. This was shown by the famous T-72A (or T-72M1) turret in the Parola Tank Museum, Parola, Finland. Tag number 5 in the photo below marks the impact of a 3BM-15 shell into the left turret cheek. Photo by Andrej Smirnov.




According to the placard (see below) at the museum hosting the turret, the shell was stopped completely after digging only 170mm through the multilayer armour. This is incredibly strange, as this would mean that the shell passed either failed to defeat the outer cast steel wall or passed through the first wall but then stopped in the "Kvartz" layer. More importantly, we do not know the range (simulated or otherwise) at which the shot occurred, and we have no idea how they determined the depth of penetration. The inner wall of the turret was obviously not cut up to examine the armour, so they must have poked a stick into the shell crater until they hit solid resistance. Since we that know "Kvartz" is a powderized material from the cut-up ex-GDR T-72M1 turret in Sweden, then it is very likely that the filler substance simply refilled the hole where the shell passed through and the measuring stick compacted the filler as it was pushed in. It would not show how deeply the tungsten carbide slug of the 3BM-15 shell entered the inner wall of the armour array. On the other hand, the statement on the placard can be interpreted to mean that the shell defeated the outer cast steel wall, passed through the "Kvartz" layer and penetrated 170mm into the inner cast steel wall, where it stopped. Either way, it is strange and most probably a typo of some sort.




Nevertheless, this example is valid enough to understand why it is often misleading to express the protection value of armour in terms of RHA steel. 3BM-15 is known to be capable of penetrating 310mm of steel at 0 degrees at 2 kilometers, but none of that performance could be seen on composite armour of the T-72A turret. Composite armour simply cannot be expressed in terms of steel equivalency, because even if you separate the  category in "KE" and "CE", you have to contend with the fact that there are are multitude of unique APDS and APFSDS penetrator designs. M735 APFSDS, for instance, has a tungsten alloy penetrator with a raindrop shape.




And the 3BM-15 along with all Soviet APFSDS designs before Vant comprised of a steel projectile encasing a small tungsten carbide slug. These penetrators will NOT behave in the same way as M735, or long rod penetrators when striking the same composite armour. As such, it would be rather foolish to assign a fixed armour value to a composite array. That said, we can still express the cast armour component of the composite armour array in RHAe, and for the T-72A turret cheeks, the cast armour is worth about 375mm RHA when we don't factor in the "Kvartz" layer. With "Kvartz", the value may be anywhere above that, but presumably somewhat more than 428mm RHA against KE threats, which is what the armour on the T-72 Ural turret was worth. Some penetrator designs may be badly affected by "Kvartz", and some may be less so.

However, the point of the composite nature of the armour was to boost protection from shaped charge warheads, so we can say with great certainty that the armour equivalency of the turret cheeks will be much, much greater than 428mm. I would say that the cheeks are equal to 550mm RHA versus HEAT warheads, because it seems like a nice, reasonable number. The resilience of the cheeks against contemporary APDS against kinetic energy projectiles of all sorts should still be very high, definitely high enough to resist 105mm APFSDS from well into the 80's. It should not, however, be able to resist 120mm DM13 at combat distances of 1500 meters, unless the composite penetrator design of DM13 is badly affected by non monolithic armour in the same manner as 3BM-15. If DM13 is indeed much worse off from not being a monobloc penetrator, then it is perfectly possible that DM13 cannot penetrate the cheeks at combat ranges or at least the upper boundaries of normal combat ranges.

According to first hand accounts on the performance of ex-East German T-72M1s during Canadian testing, found here, new experimental 105mm shells, presumably designed in the late 80's, claimed to be "jazzed up" to match 120mm rounds in performance, failed to perforate the turret armour. Apparently, the impact only formed a "slight [dinner] plate sized bulge in the armour and cast some paint flakes around the turret wall". 

The hull armour fared slightly worse, but still quite respectably. These tanks were probably fitted with the 16mm appliqué armour plate. If true, these tests echo the initial relationship between M111 "Hetz" and the T-72A, as "Hetz" was able to defeat the glacis armour at close ranges, while the turret was effectively invulnerable.


The T-72A introduced steel-reinforced plastic side skirts (interwoven textile skirt), which provided complete coverage for the sides, excluding the roadwheels. They were mounted 610mm away from the side of the hull, and could thus still drastically reduce a shaped charge warhead's effectiveness when fired at a steep angle, though certainly not to the degree that the gill armour configuration could achieve.





In general, "soft" side skirts like the type which the T-72A uses do not provide enough protection from serious shaped charge warheads at most angles of attack. At angles of 30 degrees or so, the amount of spacing provided (1220mm angled) would be enough to dissipate the cumulative jets from most tube-launched HEAT grenades and ATGMs of the 50's and 60's enough that the 80mm of side armour (160mm when angled) might be able to handle them, but the chances of even such modest hopes are slim.


KONTAKT-1




Kontakt-1 is a type of ERA first introduced in 1982. Upon beginning mass production, the Soviet army immediately embarked on a large scale upgrading programme in 1983 to equip all tanks in active service with the new ERA. The extensive programme saw the majority of T-72 tanks outfitted with Kontakt-1 within the year, and almost all tanks were outfitted by the end of the 80's. 

There are two types of Kontakt-1 blocks - full sized and reduced size. The reduced size block is used to protect special areas of the tank, like behind the headlights.

Mounting the blocks are easy. Each one is bolted onto a tinny spacer mounted all over the surface of the hull and turret. The ease of installing and replacing the blocks meant that the entire modification could be done as part of regular scheduled maintenance. However, simplicity comes at a price in this case. The ERA boxes are rather fragile, and can be quite easily knocked off when the tank is travelling through densely wooded areas, or perhaps traversing obstacles in urban sprawl. This is perfectly illustrated by the example below:




Kontakt-1 utilizes two angled explosive sandwich plates, designated 4S20, to disrupt cumulative jets through the separation of the steel plates sandwiching the explosive plates and the separation of the steel walls containing the explosive plates. It is sometimes claimed that the large number of small gaps between the individual blocks leaves a statistically large portion of the tank surface vulnerable, but this is only partially true. This is examined in the diagram below, taken from "Защита Танков" (Protection of Tanks) by V.A Grigoryan. The column of numbers to the left indicates the number of reactive plates that a shaped charge jet must pass through depending on the point of impact. As you can see, even if a warhead impacted the edge of one of the Kontakt-1 blocks, the design of the blocks is such that the jet must pass through at least two 4S20 elements. If a warhead impacted the middle of a Kontakt-1 block, the shaped charge jet will intersect with the 4S20 element of the first block, and then continue into the next block, where it will intersect with both 4S20 elements.




At the angle of installations on the upper glacis and on the turret cheeks, the 40mm gap between the Kontakt-1 blocks does not significantly weaken the overall protective qualities of the entire set. The overlap between the blocks when viewed frontally is also sufficient to counteract edge effects (shaped charge jet impacting the edge of the ERA plate).

From a frontal perspective, Kontakt-1 provides uncompromising coverage despite the presence of gaps between the individual blocks. The same can be said of the blocks installed on the sideskirts. It is obvious that the height, angle and spacing of the reactive armour package was tailored specifically for an installation angle of 68 degrees, and problems arise when the blocks are installed as smaller angles than that. As long as the blocks are installed at the appropriate angle, there are only a few circumstances in which the gaps between the blocks become weak points, and even so, they are quite small.


Each Kontakt-1 block consists of two 4S20 explosive elements, which are plastic explosives packed into a flat steel plates. The 4S20 elements are arranged in a V-shape with an angle of 9 degrees between them. The mass of the explosive material in each element is 260 grams, equivalent to 280 grams of TNT. They are high insensitivity to ensure that they can survive rough handling, being hit by machine gun fire, autocannon fire, set aflame in napalm and anything else as long as it is less powerful than a shaped charge. Kontakt-1 is so safe from external damage that the one thing that you will always notice with destroyed tanks clad in Kontakt-1 is that even if they are completely burnt out from a cook-off of catastrophic detonation, all of the ERA boxes will survive intact. Here are some examples:



Kontakt-1 on this T-72B:




And this Georgian T-72B:




And on this Georgian T-72AV:




The plastic explosive contained inside the 4S20 explosive elements are especially insensitive compared to later reactive armour explosives as a matter of necessity, because Kontakt-1 blocks lack a thick protective front plate like Kontakt-5, ERAWA-1/2 and Relikt. This is the main reason why Kontakt-1 has absolutely no effect on KE rounds - they are so insensitive that they fail to detonate when hit. The low sensitivity also makes Kontakt-1 easier to defeat by tandem warheads using the non-initiation approach.

The weight of each block is 5.7 kg, while the reduced size block weighs slightly less. A full set covering the entire tank weighs approximately 1.2 tons. The 4S20 explosive elements can be removed from the block by simply unbolting it, essentially leaving empty metal boxes bolted to the tank. This was always done as a safety precaution when putting tanks into long term storage. 



Kontakt-1 is extremely easy and simple to install. All that are needed are some bolts and nuts.



METHOD OF OPERATION



When a cumulative jet passes through the explosive elements, the resulting explosions will propel the walls of the box at a very high velocity at oblique angles to the jet, thereby cutting off most of the body of the jet. Compared to the Israeli Blazer ERA, Kontakt-1 is much more powerful, has more flyer plates, is better angled, much less sensitive to changes in angle, and has a more optimized sandwich arrangement.





Each individual 4S20 explosive element is technically considered an explosive reactive armour panel by itself. In Russian nomenclature, each explosive element is classified as a so-called "Dynamic Element", as it can work adequately on its own, like "Blazer", for example. The explosive element consists of of two medium hardness steel sheets sandwiching a layer of plastic explosives. The steel box containing the two explosive elements has walls measuring 3mm thick. The steel box does not merely function as a container for the explosive elements; it also contributes to the overall disruptive effect against shaped charges when the explosive charge is detonated. 


The thicknesses of the three layers of 4S20 is not disclosed, but from the photo above, it appears that the ratio of the thickness of the steel plates sandwiching the explosive layer thickness is 1:2. By scaling the known thickness of a full 4S20 plate to the 3mm walls of the steel box, the thickness of the steel sheets should be around 2.3mm or less, while the PVV-5A plastic explosive layer is around 5.4mm or more. This means that 4S20 has a slightly better ratio of flyer plate thickness to explosive layer thickness compared to "Blazer" ERA, which had a simpler 3/3/3 steel-explosive-steel sandwich configuration according to ointres.se. This would be a 1:1 ratio.

Using the known characteristics of the PVV-5A plastic explosive used in 4S20, we can apply the Gurney equation for symmetric sandwiches to calculate the velocity of the flyer plates. As mentioned before, the mass of a complete 4S20 element is 1.35 kg, while the mass of the explosive charge is 0.26 kg. The mass of the flyer plates sandwiching the explosive layer is obtained simply by subtracting the mass of the explosives from the total mass of the sandwich. The detonation velocity of PVV-5A is 7400 m/s, so we obtain a Gurney constant of 2.46 km/s. From all this, the velocity of the flyer plates is predicted to be approximately 1.156 km/s. The Gurney method of predicting plate velocities is detailed in "Gurney Energy of Explosives: Estimation of the Velocity and Impulse Imparted to Driven Metal".


In "Stopping Power of ERA Sandwiches as a Function of Explosive Layer Thickness or Plate Velocities", Dr. Manfred Held observed that the performance of 1mm thick flyer plates increased exponentially as the explosive layer increased, concluding that the increases in the flyer plate velocity is responsible for the increased performance. 

This is further supported by the theoretical model proposed by Yadav in "Interaction of a Metallic Jet with a Moving Target". Yadav's model showed that the magnitude of the reduction of penetration of a shaped charge jet was primarily affected by the velocity of the flyer plate, and not by the density of the plate, and that by increasing the ratio of explosive charge thickness to the flyer plate, the penetration of a shaped charge jet could be reduced. A reduction in the density of the flyer plates resulted in an increase of performance due to the subsequent increase of the velocity of the plate. 


Held states that the experimental data obtained by M. Ismail in "Optimization of performance of Explosive Reactive Armors" using 1-3mm flyer plates and explosive layers with thicknesses ranging from 2-5mm fits well into his model, to his surprise. Since access "Optimization of performance of Explosive Reactive Armors" is not currently available, the reproduction of Ismail's data in Held's paper is extremely useful. As we can see in pages 235 and 236, the reduction of residual penetration of shaped charge jets plateaus between explosive layer thicknesses of 2-5mm with both Held's 1mm flyer plates as well as Ismail's 3mm flyer plates. From this data, we can predict that the 2.3/5.4/2.3 configuration of Kontakt-1 should achieve something close to the maximum performance possible from a symmetrical sandwich layout, considering that PVV-5A is slightly weaker than the explosives used by Held.


According to an NII Stali information placard, the dimensions of a 4S20 explosive element is 252x130x10 mm. A complete Kontakt-1 block measures 314 x 148 mm overall, including the sheet metal flaps at each end of the block for attachment bolts to pass through. There are two variants of Kontakt-1 blocks, as you can see below. Diagram taken from "Защита Танков" by V.A Grigoryan.



Stock footage and stills of a Kontakt-1 block being disassembled are available here (link). Disassembly and the removal of the explosive elements can be done with a simple wrench.


The V-shaped arrangement of the 4S20 elements inside the Kontakt-1 block was a unique Soviet development and was substantially more advanced than any other reactive armour configuration available anywhere else in the world at the time. The research paper "A numerical study on the disturbance of explosive reactive armors to jet penetration" penned by a team of Chinese researchers, gives us a good look into how Kontakt-1 would work. The research, which was funded by the Chinese Ordnance Society, involved testing reactive armour on armour plate inclined at an obliquity of 68 degrees using a 54mm shaped charge warhead with a copper liner. This oddly specific angle hints that this research was perhaps part of a Chinese evaluation of the performance of Soviet reactive armour on tanks like the T-72, which had an upper glacis plate sloped at 68 degrees. We can learn much from it as well. The paper describes the effects of a single layer of ERA placed at oblique angles of 45 degrees to 68 degrees under subheading 4.2. Here are the relevant paragraphs, given verbatim:


"4.2. Oblique penetration

The typical interaction patterns of the jet penetrating into ERA and main target at an impact angle of 68° are shown in Fig. 7. Compared with the normal penetration shown in Fig. 6, the reactive armor disturbs the jet more significantly during oblique impact. When the explosive of ERA is detonated, the outward movements of the plates cut the jet directly, thus severely disturbing the penetration process. With the formation of more jet segments as a result of the continuous interaction, the residual penetration capability is reduced significantly. It can be seen from Fig. 7 that, when the disturbed jet penetrate into the plate at a larger impact angle, its tip slides along the surface of the rear plate, resulting in bending, breaking, and scattering the jet (segments). Thus the depth of penetration into the main target is significantly reduced."

"It can be seen from Fig. 9 that the greater the impact angle is, the shallower the penetration depth is. In addition, the penetration depth is reduced significantly when the impact angle is more than 45°. The penetration depth is reduced by 55%–75% in the range from 45° to 68° (impact angle) with respect to case without ERA"


This is Fig. 9:




As you can see, a single layer of ERA with a design similar to a 4S20 cell (if not exactly the same) can provide a 75% decrease in penetration at 68 degrees obliquity. But Kontakt-1 is a V-shaped design. How would that fare? Let us take a look under subheading 5.2:


"5.2. Influence of impact angle

Fig. 11 shows the predicted results of main target penetration for the cases with and without 9° V-shaped ERA at various impact angles. It can be seen from Fig. 11 that the penetration capability is reduced by 60%–90% for the range of impact angles studied. Fig. 12 shows the penetration holes of the disturbed jet penetrating into the main target. It is shown that the penetration path is deviated, and the deflection increases with the increase in impact angle. The diameter of the hole, especially at the entrance, becomes larger with the increase in impact angle. Similar to the case of flat ERA described in Section 4.2, the former and the latter are probably caused by the bend of jet and the decentralization of jet, respectively."


Fig. 11 is show below:



With a V-shaped design, the pair of ERA layers, or elements, can reduce the penetration of a shaped charge by 90% at 68 degrees obliquity. According to a fact sheet from NII Stali, Kontakt-1 can reportedly reduce the penetrating effects of cumulative jets by an average of 55% at 0 degrees obliquity, and up to 80% when angled at 60 degrees. Based on this, increasing the obliquity to 68 degrees could easily garner a 90% reduction, so we have complete justification to treat the Chinese V-shaped ERA as an exact replica of Kontakt-1. 


Furthermore, NII Stali claims that Kontakt-1 can reduce the penetration power of a typical anti-tank missile, using the Konkurs as an example (130mm diameter) by up to 86%, or 58% for a 125mm HEAT shell, or up to a whopping 92% for smaller sized warheads like the one on the 66mm LAW. We can only assume that these are for 60 degree impacts, and not 68 degrees. It is not exactly known why a 125mm HEAT shell would fare so much better than even an anti-tank missile with a much large shaped charge diameter (the 125mm HEAT shell has a thick casing, so the actual diameter of the shaped charge inside it is only 105mm). A plausible explanation is that the thick-walled spike tip/probe partially protects the tail of the jet when the reactive armour block is detonated and the flyer plates are propelled into the path of the jet.


The details of why the explosive elements are arranged with an angle is examined under subheading 5.3. The research shows that the maximum performance of the ERA can be obtained if the two elements are arranged parallel to each other, but if a shaped charge impacts at 0 degrees obliquity to ERA with such an arrangement, the effect will be absolutely minimal. Since practical experience shows that tanks are not always hit where it is toughest, the V-shape of the experimental ERA would give it better performance in low obliquity hits. Where a simpler single cell ERA may be of minimal value at low obliquity, a V-shaped ERA like Kontakt-1 may still perform its duties with an acceptable loss in performance. But why 9 degrees specifically? The paper explains that varying the angle between the ERA layers does not significantly change the performance of the reactive armour. Here is the relevant excerpt:

"However, the variation of penetration depth with increase of V-angle is quite small. It is observed that the penetration depth is reduced by 85%–90% for all the studied V-angles. Therefore it is demonstrated that the reduction of the penetration depth is not sensitive to V-angles investigated in this paper."

Note that the researchers tested angles of 0, 5, 9, 13, 17, and 21 degrees. 

Here are X-ray photos and simulations of the passage of a shaped charge jet through the V-shaped ERA at a 0 degree obliquity. Even at 0 degrees, the disruptive effect of the ERA is substantial.






Now that we have covered the working mechanism of Kontakt-1, it is important to note that it is not only used to protect the tank from frontal attack. The addition of Kontakt-1 blocks is also important for a different reason, which is that the crew now becomes much better protected from tube-launched or air-dropped shaped charge bomblets and submunitions, though the hatches are not protected. It does not matter very much that ERA blocks have a much smaller obliquity relative to a vertically descending bomblet when mounted on the turret roof, which is almost but not flat, because all small-sized HEDP bomblets have very low armour penetration. Even if penetration is achieved somehow, the after-armour effects from the highly degraded cumulative jet will be pitiful at best. The only disadvantage is that there are numerous gaps between the Kontakt-1 blocks, so the roof of the T-72 cannot be considered immune to such attacks.





T-72B




The T-72B and the series it spawned represented a very significant step in the evolution of the T-72, with the introduction of bulging armour in the hull and turret. Bulging armour is a type of non-energetic reactive armour (NERA), meaning that it is a reactive armour having the effect of degrading the projectile rather than only passively resisting it. This will be explained in an expository section below. The T-72B is also notable for being the first T-72 to incorporate an ERA package as part of its original factory configuration. That is, all T-72Bs were built with Kontakt-1 installed.



Glacis


The glacis array of the T-72B represents the first major update since the original type found on the T-72 Ural. The thickness of the armour remained practically the same after the first update in 1976 with the introduction of the Ural-1. The spaced armour array of the T-72B may have significantly better protection from KE projectiles than the NERA arrays used in its NATO adversaries, but significantly worse shaped charge protection. Nonetheless, this was fully compensated by the use of Kontakt-1 reactive armour.

The illustration below was prepared by Otvaga and Tank-Net user Wiedzmin, and is confirmed to be correct using photographic evidence.






Arrays 4, 5, and 6 refer to the glacis configuration of the T-72B models obr. 1983, obr. 1985 and obr. 1989 respectively. Here is a listing of each layer, translated from the original claims.


Obr. 1983 / Transitional

60mm RHA + 15mm Air Space + 15mm HHS + 15mm Air Space + 15mm HHS + 15mm Air Space + 15mm HHS + 15mm Air Space + 50mm RHA (215mm Total)

 Obr. 1985 

60mm RHA + 10mm Air Space + 10mm HHS + 10mm Air Space + 10mm HHS + 10mm Air Space + 20mm RHA + 10mm Air Space + 20mm RHA + 10mm Air Space + 50mm RHA (220mm Total)
  

Obr. 1989

60mm RHA + 35mm NERA (5mm Rubber + 3mm RHA + 19mm Air Space + 3mm RHA + 5mm Rubber) + 60mm RHA + 10mm Anti-Radiation Layer + 50mm RHA (215mm Total)



The first and second T-72B versions incorporated simple spaced steel armour in different configurations, but a pair of bulging plates was finally implemented in the 1989 model. Before we go into detail, be reminded that the T-72B is always outfitted with Kontakt-1, and the 1989 variant is always outfitted with Kontakt-5. Only a few T-72Bs went into service without Kontakt-1, and it appears that these variants were exclusively used for Victory Day parades only. It is very likely that they were special parade models that never had Kontakt-1 installed, although it would be very straightforward to add it on at a later time. Note that the T-72B entered service in 1984 and began serial production in 1985, so the most relevant variants are the obr. 1985 and obr. 1989. The pre-production model (Obr. 1983) has been described as a transitional model of the T-72A, and was only produced in small numbers.


BTK-1Sh steel is possibly used in lieu of the usual 42 SM medium hardness steel for the thicker plates of the upper glacis array, and also possibly for the side hull armour as well. It is known that BTK-1Sh was used in the hulls of late production T-64A tanks since 1973 - 1975, and in the hulls of T-64B tanks since the beginning of production in 1976. The T-80 tank also makes extensive use of this steel in the hull, while the cast turret of the T-80U contains thick plates of the steel within the armour cavities.

BTK-1Sh steel is a high strength steel produced by electroslag remelting (ESR), giving it higher hardness than normal medium hardness steel while maintaining a good level of ductility to prevent brittle failure when struck. According to Andrei Tarasenko, the steel BTK-1Sh is used in the turret of the T-72B, but it is very likely that it was used in the hull of the T-72B as well because BTK-1Sh was explicitly stated to be used in the hull of the T-80 tank according to this document. In general, BTK-1Sh is recognized as a general purpose high strength steel, suitable for welding (according to the aforementioned document, which dealt with the weldability of the steel) and for manufacture in thick plates of up to 85mm, or perhaps more. Depending on the thickness of the plate, the hardness of the steel ranges from 400 to 450 BHN. Tarasenko asserts that the resistance of BTK-1Sh is around 5-10% more compared to RHA steel against subcaliber projectiles at angles of 68 to 70 degree, but the type of subcaliber projectile is not specified. It is likely that the "subcaliber projectile" refers to tungsten alloy long rod penetrators.

That said, there is no confirmation that the T-72B uses BTK-1Sh in the hull. Nevertheless, the implementation of this improved steel by 1985 is to be expected, seeing as BTK-1Sh has been used in the production of welded hulls since the early 1970's.


The steel used for the high hardness spaced plates is unclear. It is possible that normal 42 SM medium hardness steel was used for the walls of the array while BTK-1Sh is used for the spaced steel plates, but it is also very possible that true high hardness steels were used for the spaced steel plates. If so, then it is highly likely that BT-70Sh steel was used, as it is treated a hardness of around 534 BHN when produced in thin plates. In fact, the patent for BT-70Sh specifically mentions that the range of thicknesses for BT-70Sh is from 15mm to 25mm. This matches perfectly with the thicknesses of the spaced steel plates in the upper glacis array. The relevant passage from the patent is presented below:

"Техническим результатом настоящего изобретения является получение листового проката толщиной 15-25 мм, обладающего высокой противопульной стойкостью в сочетании с пониженной склонностью к образованию вторичных осколков, повышенными характеристиками прочности и твердости при достаточной пластичности и вязкости, что позволит увеличить надежность защитных конструкций."


The translation (using Google Translate, and proofread):


"The technical result of the present invention is the production of sheet steel with a thickness of 15-25 mm, having high ballistic resistance combined with a reduced propensity to form secondary fragments, increased strength and hardness characteristics with sufficient ductility and viscosity, which will increase the reliability of the protective structures."


BT-70Sh is also manufactured using ESR technology, and is suitable for welding, as proven by its usage in the BMP-2 infantry fighting vehicle. However, the spaced steel plates of the armour arrays described for the Obr. 1983 and Obr. 1985 variants are not secured to the side hull plates by welding but are suspended by spacers, as we will see later.

Without clear answers regarding what steel is used in the T-72B, we shall divide our attention to two possibilities:


  1. A conservative estimate where 42 SM steel is used for the thicker plates, including the side hull armour, and BTK-1Sh is used for the spaced steel plates.
  2. A progressive estimate where BTK-1Sh steel is used for the thicker plates, including the side hull armour, and BT-70Sh is used for the spaced steel plates.



Obr. 1983




The photo above shows a destroyed T-72 from the first Chechen war. The glacis array of a different destroyed T-72 is visible down at the bottom half of the left side of the photo - it is the ramp on which the tracks are laid upon. Apparently, this array is used by a transitional variant of the T-72A built in around 1983. Note that the spaced steel plates are not welded to the side hull walls which the thick front and back plates are welded to. Rather, the spaced steel plates are held by spacers, presumably with the intention of ensuring proper spacing between the plates.

We will not be examining this array in much detail, because the T-72B obr. 1983 is not a common variant and does not represent the T-72B as a whole. Our analysis will be focused on the Obr. 1985 variant. That said, there are some preliminary observations we can make of the Obr. 1983 glacis array that hold true for all of the other variants.


This array design is a good example of a Whipple Shield; a multi-layered spaced armour array comprised of multiple thin steel plates. Some of the protection value of the array may come from the interference of a shaped charge jet or a long rod projectile by the "lips" formed at the edges of the perforated plates, which are deflected from the neighbouring plate and into the path of the penetrator. The photo comes courtesy of Militarysta from the Polish militarium.net forum.




According to Militarysta, it was noted that only slightly better results were observed at high angles of obliquity, and that an improvement can be gained by packing more spaced plates in a smaller space. It is inferred that the additional protection offered by the intersection of the "lips" with the body of the cumulative jet is rather low, and would be an inefficient method of employing spaced armour, especially for the T-72B, as there are only three (!) spaced plates in the array, and the ratio of plate thickness to air gap size is one to one. The back surface of the heavy 60mm front plate and the front surface of the 50mm back plate would also have some effect, but overall, the contribution of the "lip" effect is obviously very minor.
Indeed, if the array in the T-72B obr. 1983 truly focuses on relying on the use of these "lips" to disrupt the cumulative jet, then it is very likely that the armour would be worse than that of the uparmoured T-72A upper glacis. Recall that the combined thickness of the steel in the array amounts to only 155mm, while the rest of the array is filled with nothing but air. An up-armoured T-72A upper glacis contains 126mm of steel, and 105mm of glass textolite, which was identified as the most optimal composite sandwich filler according to NII Stali. The design of the armour of the T-72B obr. 1983 does not hold up even if we make the conservative assumption that the spaced plate array maintains the same resistance to shaped charges as the T-72A but has improved ballistic resistance against long rod penetrators.

Therefore, the theory that the spaced armour for the T-72B obr. 1983 relies on "lips" for increased protection is a completely insufficient explanation, and does not justify the change from a glass textolite filler to a spaced plate array. We will further examine spaced armour in more detail in the section regarding the Obr. 1985 array. 



Obr. 1985




The photo above shows the exposed glacis armour of a damaged T-72B3, taken during the 2015 Tank Biathlon. As you may recall, the T-72B3 program refurbishes and modernizes old T-72Bs. The vast majority of T-72B in the Russian army are Obr. 1985 tanks, so it should be no surprise that the vast majority of T-72B3s will have the same base armour. 

The total thickness of this array is 220mm, which is only 5mm more than the 60-105-50 array of the T-72A, and the amount of steel in the array is increased from 110mm to 170mm. The total thickness of steel is also greater than in the Obr. 1983 array; at the 68-degree angle of the upper glacis, the physical LOS thickness of the Obr. 1985 array is 434mm.


Again, it is very obvious that the spaced steel plates are not welded to the side hull armour plate by looking at the photo below. Note the jagged edges of the front and back plates and on the lower glacis plate. This is evidence of welding. The spaced steel plates, on the other hand, are clean. The spacing between the plates is presumably maintained by spacers similar to the type seen on the Obr. 1983 variant, but they appear to be removed in the photo below. This explains why some of the plates are in contact with each other, whereas the plates seen in the photo above clearly show uniform spacing between the plates. The spacer was presumably removed for the tank in the photo below, probably because it was about to be scrapped.




The glacis array of T-72B obr. 1985 is similar to the early obr. 1983 version, but probably more effective due to a more nuanced design. If the thin spaced steel plates are made from BT-70Sh steel, they will have a very high hardness of around 534 BHN, and the heavy front and back plates would have a hardness of 450 BHN if BTK-1Sh is used. If BTK-1Sh is used for the spaced plates instead of BT-70Sh, then the hardness of the spaced places will be around 450 BHN, while the heavy front and back plates plates would remain the softest at 340 BHN if 42 SM steel is used. 


One conceivable weakness is that long rod penetrators would find it easier to penetrate the spaced plates due to the low thickness and high obliquity. However, further inquiry reveals that sloped armour plates at such high obliquity are effective at fracturing and defeating long rod projectiles under the right conditions.

The 60mm front plate is intended to particulate shaped charge jets and to fracture and erode long rod penetrators before they can enter and interact with the spaced armour array. The relatively high thickness of the front plate is meant to effectively particulate shaped charge jets. The same reasoning applies for long rod penetrators; long rod penetrators are generally capable of penetrating more armour at higher obliquities than at lower obliquities, so the steep 68 degree angle of the upper glacis is ostensibly disadvantageous, but that is not the case here. Long rod penetrators are susceptible to fracturing after perforating oblique armour plates, especially at very high angles. This is due to the asymmetric buildup of stress within the tip of the rod during penetration, which is immediately released once the rod emerges from the back surface of the plate. The release of stress fractures the rod at the tip, and the asymmetric forces also deflect the rod sideways or downwards. The fracture also tends to be diagonal to the axis of the rod due to the asymmetry of forces acting on the rod as it penetrates through the rear portion of the sloped plate, caused by the greater relative thickness of the sloped plate in the region above the rod and the lower relative thickness below the rod. Thicker plates are more effective and more reliable at producing fractures because the longer duration of penetration causes a bigger buildup of internal stress in the rod, leading to a more severe fracture once the rod exits the back of the plate, but thinner plates can be used in this capacity as well.


The paper "The Penetration Process Of Long Rods Into Thin Metallic Targets At High Obliquity" by Yaziv et al. helps us to understand the functions of the spaced steel plates in the array. The experiments and numerical simulations were conducted at target plate angles of 70 to 80 degrees, with two of the numerical simulations having been conducted at angles of 73 and 76 degrees. The angles are slightly higher than that of the upper glacis of the T-72B, but it is still perfectly acceptable to apply the results to the armour array, as the same obliquity can be achieved on the T-72B by simply angling the hull to the side by a few degrees. High hardness steel plates with a yield strength of 1200 MPa were used in the simulations and in both experiments (A and B).

The long rod penetrators were detailed as being 135mm long with a length to diameter ratio of 17, denoting that the diameter of the rod is 7.94mm. The plates had a thickness ranging from 7mm to 13mm - closely equivalent to the diameter of the long rod penetrator. The L:D ratio of the tungsten alloy rod is slightly better than that of the 120mm DM23 APFSDS round (1983), and the rod has a slightly tapered frustrum that matches the profile of common tungsten long rod projectiles.




The tip of the rod ricochets on impact with the plate and shatters into fragments, and only the central part of the rod actually does the work of penetrating the plate. As the central part of the rod penetrates the plate, it is deflected downwards and begins to rotate as it emerges from the plate. These effects are apparent on armour plates at lower angles of obliquity as well, and generally become significant at angles of more than 60 degrees. The ricocheting of the tip of a tungsten alloy long rod becomes very apparent at a target plate obliquity of 75 degrees, and increases in severity until the critical ricochet angle of the projectile is reached, whereby the entire rod ricochets off the plate and not just the tip. 

The downward deflection of the central part of long rod projectiles is caused by a bending moment exerted on the rod due to the non-uniform thickness of plate material above and below the rod as it travels through the sloped plate. The deflection effect occurs at any obliquity and is manifests as a fracture on the rod that promptly detaches from the rest of the body. "Experimental and Numerical Simulation Analysis of the Impact Process of Structured KE-Penetrators onto Semi-infinite and Oblique Plate Targets" offers a more concise explanation of the loads experienced by a long rod projectile as it penetrates an oblique plate.


"During the perforation process  the maximum bending moments occur at the tip of the projectile. This corresponds to a situation where the penetrator can be regarded as a cantilever beam with a fixed tip region and the inertial forces acting as loads leading to the typical concave bending of the  projectile ... bending dominates the structural loads during the perforation process of KE projectiles."


The bending moment also introduces a downward velocity component to the rod, and thus induces yaw. The severity of the yaw for tungsten alloy rods depends on a variety of factors, including: The momentum of the rod, the thickness to diameter ratio between the target plate and the rod, the obliquity of the target plate, and the length to diameter ratio of the rod. It is very important to note that this phenomenon could be avoided if a separate heavy alloy segment is added at the tip of the rod, so that the tip of the rod suffers most of the effects of the ricochet and sustains the bending moment during the penetration process described in the citation above, whereupon it detaches from the rest of the rod. Because the tip segment is separate from the main rod, the main rod does not get bent or yawed in any way, and maintains the shape of its own tip. There are very few heavy alloy long rod projectiles that feature a separate segment at the tip of the main penetrator, one of them being the BM-42 "Mango".



The rear 55% of the long rod penetrator remains mostly intact during the penetration process and emerges unmolested from the highly sloped plate. As a result of the interaction with the thin sloped plates, the penetration power of the rod is reduced by 50%. The results of this study are supported by "Oblique Impact of Elongated Projectiles on Massive Targets" by Veldanov et al. and "Ricochet of a tungsten heavy alloy long-rod projectile from deformable steel plates" by Woong Lee et al., and multiple other studies.

From this, it is easy to see the advantage of multiple spaced plates of high hardness steel. The actual penetration of the plate itself only erodes and deflects 18% of the rod, whereas a much larger segment of the rod (27%) was lost from ricocheting and shattering on impact with the surface of the plate. This effect can be harnessed by arranging multiple plates at high obliquity to repeatedly degrade the long rod penetrator with each successive impact. The size of the air gap between the plates is has no significant effect on the integrity of the rod, because a sideways force component is generated during penetration, so the rod is already deflected as it emerges from the plate. However, this does not mean that the size of the air gap is arbitrary; one of the functions of the air gap is to allow the tip of the rod to ricochet up and away from the plate and to allow the shattered fragments of the tip to be ejected away. Increasing the size of the air gap also gives more time and space for the rod to rotate and yaw before it impacts the next plate, but the amount of space needed to produce a useful reduction in the penetration power of the rod is impractical for tank armour.



In the T-72B obr. 1985, the first two plates are of high hardness but are only 10mm thick, so the thickness of the plates would be smaller than the diameter of virtually all long rod penetrators for tank guns. These two plates will be deformed by the impact of a long rod penetrator, but it is not yet clear how they contribute to the overall scheme.


The last two plates, measuring 20mm thick, should have the effect of further destroying the long rod penetrator, which should be severely degraded and somewhat deformed by this point. These two plates best agree with the experimental parameters in the paper by Yaziv et al. and can be considered direct analogues, so a long rod penetrator could very possibly lose up to 50% of its residual penetration power after passing through one of these plates, its residual penetration power being its penetration power after passing through the heavy front plate and two thin spaced plates.


Scientific studies have shown that the propensity of the tip of the tungsten alloy long rod penetrator to ricochet and shatter on impact with an oblique armour plate depends greatly on the hardness of the armour plate. The description of the high hardness plate in the paper by Yaziv et al. is consistent with armour plates with a hardness between 400 and 500 BHN, making the conclusions from the paper compatible with BTK-1Sh steel, but if BT-70Sh is used instead, then the protection level offered by the array increases astronomically. According to the patent for BT-70Sh, the maximum strength of the steel is between 1900 to 2000 MPa when treated to the maximum hardness of 54 HRC (543 BHN). This greatly surpasses the strength and hardness of the steel used in the simulations and experiments, and would have yielded even better results.


This array design should be adequate for APFSDS shells appearing in the early 80's such as the 105mm DM23 and DM33 at 1 km or perhaps less. This estimation is based on the knowledge that DM23 is a licence produced version of the M111 "Hetz", and that the reinforced T-72A glacis array is already sufficient to resist the M111 even at short range, and the DM33 simply has a more elongated penetrator. Composite shells like the 120mm DM13 (1979) and DM23 (1983) will not perform well against this array, and will most likely fail to penetrate even at a distance of 1 km. The longer DM33 round (1987) with 480mm of penetration at 2 km (according to the manufacturer, as stated in this document) will be sufficient at combat ranges of 1.5 km, but the reliability of the shell may be uncertain if the hull is angled slightly.


In short, the ballistic resistance of the spaced armour should be very high. However, the resistance of the armour to shaped charge threats mainly depends on the raw physical thickness of the steel, and is nowhere close to the level of protection offered by Non-Energetic Reactive Armour (NERA). 



AGAINST SHAPED CHARGES



After learning about how the side skirts on a tank may increase the standoff distance of a shaped charge jet and thereby increase its penetration rather than decreasing it, it seems counter-intuitive that the T-72B uses multiple spaced armour plates in the upper glacis array rather than evolving the simple composite sandwich from the T-72 Ural (originally from the T-64A) into a multilayered steel and glass textolite array like the T-64BV or T-80BV, but as is often the case, the terminology is misleading as not all spaced armour is the same.

From what we have seen of the original T-72 Ural and T-72A composite armour sandwiches, it is known that the heavy front plate of the array is intended to particulate a shaped charge jet before it enters the low density glass textolite filler, thus maximizing the performance of the filler. The chief concern with side skirts acting as standoff for shaped charges is that the skirting is too thin or too light to particulate a shaped charge jet, so it emerges as a continuous, undisturbed jet and gains increased penetration power as it stretches in the air gap. When a side skirt of sufficient thickness is used, the jet is particulated as it emerges, meaning that it ceases to stretch and the jet splits into individual particles as a result of the velocity gradient along the body of the jet - the tip is the fastest, so it separates from the segment behind it because it is slower, and that segment is slightly faster than the segment behind it, so it separates, and so on - this is avoided in a continuous jet because the entire jet is accelerating forward. 

The heavy 60mm front plate of the T-72B is still thick enough to particulate a typical shaped charge jet, so the penetration of the jet cannot possibly increase. This resolves the issue of spaced armour acting as standoff for a shaped charge warhead. However, having air instead of a low density filler makes the armour inefficient against shaped charge jets. As mentioned before, a brief explanation on the NII Stali stated that a low density nonmetallic filler sandwiched between two steel plates was the most optimum configuration at angles more than 60 degrees, and having an air gap instead of a nonmetallic filler gave the worst results of all. In this context, the spaced steel array in the T-72B obr. 1985 appears to be a step backwards, but this is not necessarily the case.

According to "Shaped Charge Attack of Spaced and Composite Armour", spaced armour can be effective against shaped charge jets due to the forces acting on the jet as it penetrates the target plate. The relevant passage is presented below:

"It has been shown [1,2] that the shaped charge jet tip is disrupted when it exits from a finite thickness plate. This is due to longitudinal and radial shock wave effects in the jet causing mushrooming of the jet tip or enhanced particulation. This effect has been utilised in the design of 'Whipple shields' which consist of multiple thin plates."

This is supported by "Spaced Armor Effects of Shaped Charge Jet Penetration", where it is stated that: 

"During the process of target perforation, the jet was compressed, which increased the jet tip diameter. Upon leaving the first target plate, relief of the compressed material occurred, which led to further expansion of the jet tip."

It was also confirmed in "Shaped Charge Attack of Spaced and Composite Armour" that there is a danger of spaced armour having the opposite of the desired effect; noting that "Conversely the ultimate warhead penetration may actually increase with spacing and/or standoff as the warhead is brought closer to an optimum standoff compared to the normally fused short standoff". Other studies dealing with spaced armour have included similar remarks, and is a legitimate concern with spaced armour. This was solved by including a heavy front plate in the glacis array of the T-72B, but it is good to have confirmation nonetheless.


A detailed examination of the effects of thin plates on shaped charge jets is provided by "The Shaped Charge Jet Interaction With Finite Thickness Targets". The paper examines the interaction of shaped charge jets with individual and multiple armour plates of finite thickness. As we already know, a plate of sufficient density and thickness can particulate a shaped charge jet as it emerges (termed "foreshortening"), but the effect of multiple spaced plates has not yet been broached thus far. The paper gives this explanation on the effect of finite thickness targets on shaped charge jets:


" ... the problem concerning the interaction of the shaped charge jet with the target whose thickness does not exceed several jet diameters as well as with a set of such targets, spaced at some distance apart from each other, is considered. The existence of air gaps between such targets lead to additional losses of the jet length due to the erosion of its tip region upon the target perforation, which was first noticed by Brown and Finch [1] and was termed "foreshortening" (forefront shortening)."


In other words, the existence of air gaps prevents us from simply adding up the physical LOS thicknesses of the individual plates to find out the nominal RHA equivalency of the armour against shaped charges. It is necessary to understand that the publicly available RHA penetration figures for shaped charges is always obtained using semi-infinite target plates - targets where the penetration of the jet does not exceed the thickness of the plate. This is the most optimal condition for shaped charges and cannot be applied to spaced armour, so for example; a shaped charge warhead with 500mm of penetration may not be able to defeat the spaced armour of the T-72B obr. 1985, even though the physical thickness of steel in the armour is only 454mm. 


The most relevant reference for us is "On Modelling of Shaped Charges Jet Interaction With Spaced Plate". The paper directly deals with spaced plates at a normal impact angle as well as oblique spaced plates and is highly expository, making it a convenient resource in analyzing the armour of the T-72B obr. 1985. The conclusion of the paper supports the previous claim that spaced armour cannot be directly compared to homogeneous plates, even though shaped charge jets penetrate both types of targets via hydrodynamic interaction. Indeed, it is explicitly stated in the conclusion that equating the two types of targets leads to an overprediction of the jet velocity in the case of spaced plates, meaning that the spaced plates reduce the velocity of a shaped charge jet by a greater amount given the same material, the same cumulative total thickness of plate material, the same standoff, and so on. The relevant passage is given below:


"It has been shown that the hydrodynamic penetration theory can be used for getting a good estimation of shaped charge performance against homogeneous steel targets, provided to know the lateral velocities of all jet elements. But it has also been shown that such modelling is not suitable against spaced targets and overpredicts the jet residual velocities after perforating metallic plates."


The paper examines and compares normal and oblique spaced plates of 10mm thickness angled at 60 degrees. Using the same penetration models (1D-code + eq. (5)) as the plates impacted at a normal angle but with the addition of a simple equation (eq. (6)) to account for the new relative thickness of the oblique plates, it was proven that oblique spaced plates behave and interact with shaped charge jets in the same manner as non-oblique plates.



It is common knowledge that shaped charges are unaffected by armour slope and will penetrate the same thickness of homogeneous armour at any angle, but this essentially proves that shaped charges are unaffected by armour slope for spaced plates as well, effectively enabling us to use other reference material that examine spaced plates but not at an angle. 


Everything considered, it is clear that the spaced armour array in the T-72B obr. 1985 is highly inefficient against shaped charge threats, but still effective nonetheless. All together, it is likely the anti-shaped charge properties of the spaced armour array are at least on the same level as the T-72A, but no lower. It is important to note that the raw physical thickness of the steel in the T-72B obr. 1985 array (454mm) already exceeds the claimed HEAT resistance of 450mm RHA of the original 80-105-20 array of the T-72 Ural. As we now understand, the peculiarities of spaced armour means that we cannot equate it with a single homogeneous steel target, so in reality, there can be no doubt that the shaped charge resistance of the spaced armour array exceeds 454mm RHA. It is very likely that it is sufficient against the majority of handheld antitank weapons, older missiles like the TOW (430mm penetration), and 105mm HEAT rounds from the early 80's like the DM12 and M456A2. 

It is very unlikely that the basic armour could resist the ITOW on its own (630mm penetration), and it definitely will not hold up to the Milan 2 (790mm) or to the TOW-2 (890mm penetration), but this is based on the assumption that Kontakt-1 is not present. Due to the installation of Kontakt-1 as standard equipment on the T-72B, the upper glacis should still be completely invulnerable to all of these missiles, and any other single-charge HEAT warhead. The use of tandem warheads would negate Kontakt-1 to a large extent, so missiles like the TOW-2A would be a serious threat to the upper glacis armour.



In conclusion, the spaced steel armour of the T-72B obr. 1985 cannot be labeled as "simplistic" or "crude". The armour is designed to make full use of a complex set of mechanisms aimed primarily at destroying long rod projectiles, and with comparable or better shaped charge resistance to the earlier pattern of composite sandwiches. The perception of spaced steel as a crude method of protection is largely invalid except when compared to NERA armour in terms of shaped charge resistance.


Obr. 1989




According to the description provided by Wiedzmin, the glacis array of T-72B obr. 1989 can be considered to be slightly more advanced on account of its meager NERA array, but it is still rather crude. It is designed to work in conjunction with Kontakt-5, which may explain the change from simple spaced plates to thicker solid steel plates. The NERA plate installed immediately behind the front plate is comprised of two opposing bulging plates, and should be equivalent to a single NERA sandwich. Against shaped charges, the NERA works by disrupting the cumulative jet (this is further discussed in the section on the T-72B turret). Against KE threats, the NERA works based on the principle of penetrator deflection and shearing. As the long rod penetrator enters the array, it activates the first bulging plate, which bulges downward, exerting downwards force on the penetrator, and as the second bulging plate is activated, it bulges upward, exerting upwards force. This exerts a shearing force on the rod.

Stopping the rest of the attacking projectile or shaped charge jet would be the the job of the remainder of the array, 110mm thick in total. The 60mm steel plate, 10mm anti-radiation layer and 50mm steel plate sandwich behind the NERA layer could technically be considered a composite armour sandwich, as the 10mm anti-radiation layer is probably made from polyethylene. Assuming the anti-radiation layer is composed of borated UHMWPE (Ultra-High Molecular Weight Polyethylene) with a density of 1.00 g/cc (density of polyethylene produced in the Soviet Union was 0.92-0.96 g/cc), then the composite sandwich should be quite decent in principle, though it might not be the most optimal configuration given the low thickness of the anti-radiation layer.

Note that the total thickness of steel in the array is 170mm, which is the same as the Obr. 1985 array. Except for the NERA plate and the anti-radiation layer, the mass of the Obr. 1989 array should be very close to the Obr. 1985 array.


The photo below confirms that the array described by Wiedzmin is indeed used on late T-72B models. Credit for all photos goes to armor.kiev.ua.





As you can see, the exposed upper glacis array matches the description perfectly. There are three solid plates, and two gaps of appropriate sizes between the three plates. Also, the rearmost plate appears to be slightly thinner than the middle plate, and this matches the thicknesses given by Wiedzmin. The tank in the photo is clearly a T-72B and most likely a T-72BA, because the tracks are UMSh tracks and not RMSh tracks, as shown in the photo below.






It is known that very late T-72A models had the T-72B turret and early spaced armour upper glacis array, but these models still used RMSh tracks. Furthermore, the exposed glacis array in the photo above looks nothing like the spaced armour array, and it is not possible that the exposed array of the tank shows the earlier STEF composite sandwich because it does not have spacer plates, like in the usual T-72A array and also in the transitional T-72A models with spaced armour.




The tank cannot be a T-72B3 either, because the disembodied turret shows four Kontakt-5 panels on the right side, where a T-72B3 would have five. A T-72BA would have four panels because the IR searchlight occupies the position next to the gun mantlet. Therefore, it is not possible that that this tank is somehow a very late T-72A model upgraded to T-72B3 standard.




According to illustrations published in Sergey Suvorov's "T-90: First Serial Tank of Russia", the T-90 has the same hull armour as the T-72B obr. 1989. The illustration below shows a T-72B obr. 1989, as identified by the presence of Kontakt-5 on the hull and the manually operated anti-aircraft machine gun. The drawing of the hull array appears to match what we now understand to be the correct configuration of the armour.





The drawing below shows a T-90, as identified by the forward-facing remotely controlled anti-aircraft machine gun and the large housing for the Agava thermal imaging sight. As you can see, the hull array is identical. Since the T-90 uses the same cast turret as the T-72B, it is safe to assume that the composition of the armour is totally identical between the T-90 and T-72B.






Turret





The November issue of the famous Russian Tekhnika i Vooruzhenie 2006 (Журнал Техника и Вооружение) magazine mentions in page 14 that the protection of the 1985 edition of the T-72B is equivalent to more than 550mm against a KE projectile. This is probably an average between the turret and the hull, but it is widely accepted that the turret of the T-72B is the stronger of the two, for reasons which we will see later on.

The turret of the T-72B - dubbed "Super Dolly Parton" by Western observers (quite a compliment) - fully retains the usual T-72 layout, with the frontal projection up-armoured and the associated changes made to the armour profile. The two primary constituents of the turret's frontal armour are the solid steel portions and the NERA array. The steel armour has a hollow cavity for the insertion of NERA plates. The front wall of the cavity is approximately 130mm thick at its thickest part (LOS), near the gun mantlet, thinning to 90mm as the turret cheek curves into the side of the turret (normal). The rear facing is composed of the 90mm cast steel wall of the turret cavity casting supplemented by a 45mm HHS rolled steel plate in front of it (pictured below). The HHS plate is most likely BTK-1Sh armour grade high hardness steel.





We don't actually know exactly how thick the cast steel is, but we know for a fact that the rolled plate is 45mm from the famous ARMOR magazine article. The thickness of the cast steel is estimated from the distance between the armour cavity and the gunner's primary sight aperture (it is recessed a bit into the armoured housing). Based on the photo below (one black/white segment = one inch) we can see that this LOS thickness is around 6 inches. Converting the LOS thickness to perpendicular plate, we can confidently say that the thickness of the cast steel is 85mm to 90mm. Combined with the 45 rolled steel plate, the total thickness of the plates behind the NERA array is a healthy 235mm.





The ARMOR Magazine article mentions that the plates inside the cavity are angled at 55 degrees from the gun barrel. As far as NERA armour goes, this is completely sufficient, and the relative angle increases as the turret is viewed from a sideways angle. The combined total weight of the contents of both cavities is 781 kg. 
The multi-stack bulging plate array of the turret consists of 20 modules. This type of armour can be considered a form of integrated NERA (Non-Explosive Reactive Armour).




Each NERA plate may vary greatly in length, but all of them are uniform in their thickness, each module being 30mm thick. The modules are composed of a 6mm rubber interlayer sandwiched between a 21mm HHS front plate and a 3mm HHS bulging plate. Andrei Tarasenko confirms that the plates are made from BTK-1Sh. The maximum length of the NERA plate is 280mm. The plates are spaced 22mm between one another by metal brackets. The entire array is angled at 55 degrees relative to the gun barrel.

The placement of the plates means that four to six plates will intersect with the direct line of fire of a projectile when the turret is being shot at head-on, more plates if the shot lands at the center of the turret cheek and less at the ends. Only two or three plates will be in the path of a projectile when the turret cheek is struck at an angle of 35 degrees. This is superior to the arrangement of the NERA plates in the front hull of the M1 Abrams, which places a maximum of four plates in the line of fire. Behind that is a spacer, which appears to provide almost no armour value as it is only there to brace the NERA plates and provide proper spacing. At best, it is a perforated steel plate, which would offer much more substantial protection, but the large size of the holes depicted in the diagram make this unlikely. Behind the spacer/perforated plate is the main armour, which is a rolled steel plate that is estimated to be about 160mm thick.






How NERA Works:


NERA was first proposed by Dr. Manfred Held in 1973 in a research paper, after inventing reactive armour in 1969 . The Wikipedia page on reactive armour has this to say about NERA:

"NERA and NxRA operate similarly to explosive reactive armour, but without the explosive liner. Two metal plates sandwich an inert liner, such as rubber.[3] When struck by a shaped charge's metal jet, some of the impact energy is dissipated into the inert liner layer, and the resulting high pressure causes a localized bending or bulging of the plates in the area of the impact. As the plates bulge, the point of jet impact shifts with the plate bulging, increasing the effective thickness of the armour. This is almost the same as the second mechanism that explosive reactive armour uses, but it uses energy from the shaped charge jet rather than from explosives.[4]"


The description of how the inert interlayer is energized by the impact of a shaped charge jet is simplified, but accurate. To be more specific, the source of energy is the shock waves travelling through the inert liner between the two metal plates sandwiching it. Here is a relevant passage from the paper "3D Numerical Simulation Of Non-Energetic Reactive Armor", quoted verbatim:

"The protective mechanism of bulging armors is slightly different than explosive reactive armors. When a shaped charge jet hits the inert intermediate layer, a shock wave interactions through the interlayer results in bulging of the metallic layers [Yaziv, Friling and Kivity , 1995], [Gov, Kivity, Yaziv, 1992], [Mayseless et al., 1993]"

The Wikipedia article's explanation of "increasing the effective thickness of the armour" is, sadly, only a half-truth at best. The research paper quoted above gives a short but concise explanation that the moving plates interact with the shaped charge jet and distort it. There is no mention of increasing the effective thickness of the armour in the paper, or in almost every other paper or journal article on NERA published in the last few decades. Dr. Held's early patents for explosive reactive armour describes the mechanism of the reduction in the penetration of a shaped charge jet as a product of the disruption of the jet. Patent 5811712 from 1975, for example, makes this very clear in the following excerpts:

"... the destruction of a hollow charge spike takes place in such a way that the spike is chopped up over large portions of its length, the individual particles of the spike being additionally diverted. The spike, of which the penetrative capacity in a homogeneous wall of steel is otherwise too high, then loses its boring power and remains in a divergent crater in armour plating following disruptor walls of this kind."

"The military effect of the invention resides quite generally in the efficient disruption and destruction of even elongated hollow charge spikes with a very high energy content and with a high velocity gradient, by the intervention of moving parts of the layer or wall in the total length of the spike ..."

"As shown by the present example, the invention makes it possible for the following charge spike, over its entire length, and despite its considerable velocity gradient, to be combated by moving walls and layers, so that by introducing material over a cutting (oblique) path into the traject of the spike the latter is completely disrupted and finally destroyed, or deprived of its boring action."


However, United States Patent 4,368,660 filed by Dr. Held in 1980 under assignment by MBB GmbH mentions the "consumption" of a shaped charge jet as an additional penetration reduction factor. Reading the "Summary of the invention" section of the patent, we see that Dr. Held describes the action of the flyer plates of the reactive armour having the purpose of "cutting up" or "consuming" or "spending" the shaped charge jet, which is referred to as a "thorn". The term "consumption" had so far never been used before when describing the action of flyer plates against shaped charge jets. Based on this, and the remarks of various scientists and academicians, it appears that Held was the first to identify the increase in effective armour thickness as a factor in the reduction of penetration. 


In 2004, Dr. Held published "Dynamic Plate Thickness of ERA Sandwiches against Shaped Charge Jets" in Volume 29 of Propellants, Explosives, Pyrotechnics, issue No. 4. Held examines the mechanism behind the generation of dynamic plate thickness and concludes that the disruption and destruction of shaped charge jets is still the main method of jet defeat by reactive armours. It is important to note that Held defined "dynamic plate thickness" as the virtual plate thickness that intersects with the path of the shaped charge jet. Held made no attempt to explain how the jet is degraded by the intersection, so his definition of "dynamic plate thickness" is merely arbitrary.

It is well known that the intersection of a moving plate obliquely against a shaped charge jet results in the loss of plate material and jet material alike through erosion. However, classifying the interaction as the penetration of the moving plate is misleading. In actuality, the moving plate is penetrating the shaped charge jet as much as the jet is penetrating the plate, so the mechanism cannot be described as simple armour penetration. The most important distinction is that the tip of the cumulative jet will almost always be on the other side of the plate before the plate even begins to move, due to the immense speed of the jet tip, so it is not the tip of the jet impacting the edges of the plate as the plate moves obliquely against it, but the midsection of the jet body. This cannot be described as hydrodynamic armour penetration. Rather, the interaction causes jet particulation, meaning that the single continuous jet is divided into smaller segments, each with their own discrete velocities. The result is that the armour plate behind the NERA plate will be impacted consecutively by two forms of shaped charge jets; a disembodied continuous jet (jet tip), and a smattering of particulated jet segments.

This is why a shaped charge jet does not penetrate smoothly into armour plate after passing through a NERA plate. Instead, shallow craters are created on a large area of the surface of the plate from the impact of the particulated jet, and some end up on the inside the deepest tunnel, which is invariably made by the disembodied jet tip. Jet particles that do not impact the tunnel made by the disembodied jet tip do not contribute to the final depth of penetration of the target plate. This is best seen in the four photographs below, taken from "Study on Rubber Composite Armor Anti‐Shaped Charge Jet Penetration". The craters were produced by a shaped charge jet disturbed by a rubber NERA sandwich plate at four different obliquities.




The greatest reduction in penetration was achieved when the rubber NERA plate was angled at 60 degrees. It is interesting to note that even at 0 degrees, the NERA plate caused some particulation to occur, as evidenced by the pockmarks around the tunnel created by the otherwise untouched shaped charge jet. In this case, the NERA plate acted as simple spaced armour, causing some of the tip of the jet to particulate due to the compression of the jet while it passes through the NERA plate, and subsequent decompression as it exits. At 30 and 45 degrees, the degree of particulation increased drastically, as evident from the much larger surface area covered with pockmarks, but the jet appears to remain somewhat unperturbed. At 60 degrees, the jet is badly disturbed by the NERA plate and is split into a number of segments. Lateral forces from the bulging plate gives the segments a sideways velocity component, causing them to impact some distance away from the main tunnel created by the disembodied jet tip.


Although Held's paper "Dynamic Plate Thickness of ERA Sandwiches against Shaped Charge Jets" deals with reactive armour, his findings can be applied to NERA to some extent. We cannot equate ERA to NERA directly in this context, of course, because the behaviour of bulging plates is simply not the same as flyer plates. The most significant differences are in the kinematics of the plates and their geometry while they are in motion. Held's calculations are based on the assumption that the flyer plate is flat and maintains a constant velocity throughout its interaction with the jet. A bulging plate, on the other hand, takes quite a lot of time to accelerate to peak velocity, and the shape of the bulging plate is curved rather than flat. Thus, the paper can be read to gain an understanding of the general mechanism of dynamic plate thickness only.




Referring to the graph above, we see that as the plate velocity increases, the dynamic thickness increases. For a rear plate (in-pursuit), there is an exponential increase in dynamic thickness against plate velocity, whereas for a front plate (head-on), the rate of increase is almost linear. Note that the velocities required to achieve a high dynamic plate thickness are well beyond the range achievable by NERA plates, so we can confidently infer that dynamic plate thickness is a very minor factor in the reduction of a shaped charge jet during its interaction with NERA bulging armour. 


For an explanation of how we can know the bulging plate velocities attainable by NERA plates, read the three research papers below:




The first paper investigates the deformation characteristics of the rubber interlayer and its ability to displace (bulge) the steel plates sandwiching it, with experiments conducted using a 3/5/3 bulging armour arrangement. The second and third papers examine the mechanisms behind the transfer of energy into the inert interlayer material of a NERA sandwich. All of the papers deal with the impact of shaped charge jets and the transfer of the jet energy into the NERA interlayer at a normal impact angle, but Rosenberg states that the motion of bulging plates is not sensitive to obliquity since the main source of propulsion is the energy transferred into the interlayer. Yadav's paper states that the amount of energy transferred into the interlayer depends on the duration of contact between the shaped charge jet and the interlayer during penetration, and on the velocity of the jet - the higher the better. Rosenberg's paper is the most convenient for us, as the bulging plate velocities for 3mm steel in-pursuit plates have already been modeled for us. Rosenberg's simulations use a 10mm plexiglass interlayer, but also investigate the effect of varying thicknesses. 





Since plexiglass is less dense than rubber, it can be assumed that the peak bulging plate velocity of the T-72B NERA at H=13.2 will be higher than the value stated in the graph. Only the peak bulging plate velocity matters to us because that is the region in contact with the shaped charge jet as it passes through. 

Rosenberg goes on to state in page 304 that NERA plates bulge faster with thinner back plates (in-pursuit) than with thinner front plates (head-on). He goes on to recommend an asymmetric NERA plate design for optimum performance. The context is that NERA plates with thicker front plates and thinner back plates will have superior overall performance, so this is not direct advocacy of the design of the NERA in the T-72B turret, but it is still strongly suggested that such a design would be advantageous as it would cause the back plate (in-pursuit) to bulge at a higher velocity. Based on Rosenberg's data on plexiglass interlayers, a reasonable guess of the peak bulging velocity of the rubber-based bulging plate of a T-72B NERA plate should be between 0.5 km/s and 0.55 km/s.


The graph below, taken from Held's "Dynamic Plate Thickness of ERA Sandwiches against Shaped Charge Jets", shows that the dynamic plate increases exponentially with increasing NERA plate obliquity. At 55 degrees, an in-pursuit flyer plate travelling at 0.4 km/s generates barely more than 50mm of dynamic plate thickness. A flyer plate travelling somewhat faster than 0.4 km/s would be able to generate more dynamic plate thickness. Based on our guess that the bulging plates in the T-72B turret have a peak bulging velocity of between 0.5 km/s and 0.55 km/s, the dynamic plate thickness offered by the bulging plate should be between 60mm and 80mm, but only if we treat the bulging plate as a flyer plate. If we do not, then the actual dynamic thickness should be much less.




Based on this information, it is clear that the primary mechanism of shaped charge jet defeat by bulging plates lies in the disruption effect of the plate. This confirms the earlier claim that the contribution of dynamic plate thickness to the anti-shaped charge capability of NERA is either negligible, misunderstood, or both.


The photos below illustrate the effect of a NERA plate on a shaped charge jet. The three photos are from three separate repetitions of the same experimental set up. Note that a substantial portion of the tip of the jet is unaffected in all three tests, and the location of the disturbed regions of the jet is consistent between the second and third photo.




The body of the jet behind the tip is disturbed due to the formation of instabilities caused by the disruption of the shape of the jet. According to "The role of Kelvin-Helmholz instabilities on shaped charge jet interaction with reactive armour plates", the disruptions experienced by the cumulative jet are Kelvin-Helmholz instabilities. Kelvin-Helmholtz instabilities are formed when there is velocity shear in the continuous flow of a fluid, namely the shaped charge jet.


There must be some space behind the NERA plate in order for it to perform at peak efficiency. This is because the perturbations to the shaped charge jet do not manifest until a small period of time has passed. Here are several X-ray photographs, taken from Dr. Manfred Held's paper "Disturbance of Shaped Charge Jets by Bulging Armour", page 194.





The photo below shows three bulging plates shot through by a high power shaped charge jet. Notice that there are keyhole-shaped cuts in the plates, and that the plates are cracked.




More energetic interlayer materials can improve the reaction speed of the NERA plates and increase the lateral energy imparted onto the jet. Rubber is the earliest and most basic material for this application, and can be considered the least sophisticated.


According to the document Multiple Cross-Wise Oriented NERA-Panels Against Shaped Charge Warheads, (the same document contains the photos above) a single NERA panel can decrease the penetration of an 84mm shaped charge warhead from 410mm to just 70mm - a reduction of 83%. Placing two NERA panels in parallel reduces the penetration by only one centimeter more, to 60mm. This seems rather odd, but is actually due to the rather simple fact that bulging armour cannot react quickly enough to intercept the tip of a shaped charge jet. Remember that the tip of a cumulative jet formed from a typical shaped charge travels at velocities of between 8 km/s and 10 km/s or more. The high velocity jet tip imparts a lot of energy into the inert interlayer, but it is simply too fast intercept and disrupt, but it is possible to cut off the rest of the jet and prevent it from doing any harm. This fact is illustrated the photo below, taken from the aforementioned document.




The very small reduction in performance offered by the second NERA plate is almost entirely due to the erosion of the jet from impacting the material of the panel (two 3mm RHA plates and one 5mm layer of rubber), not by the movement of the plates. This was because the body of the shaped charge jet had been disrupted by the first NERA plate, leaving only the disembodied jet tip to continue. The disturbed jet body could not contribute to the final penetration depth, as many of the particles were stopped on impact with the second NERA plate. More importantly, however, this tells us that NERA plates alone are not enough to stop shaped charges. The hypervelocity jet tip is too fast to be affected by the movement of the NERA plates, and can only be stopped by erosion against a solid plate. This is why it is always necessary to install an armour plate behind a NERA array. This also shows that there are diminishing returns past a certain number of layers of NERA plates in an armour array, so it may not be beneficial to install so many plates and neglect the base armour.


Moreover, the efficacy of NERA panels will depend on the material of the bulging plates as well. The document "Combination of Inert and Energetic Materials in Reactive Armor Against Shaped Charge Jets", gives us some perspective. A rubber-based NERA panel was also involved in their testing. However, their NERA panel could only effect a 22% reduction in penetration performance for a 64mm shaped charge warhead. Where did the 61 percentage point difference go? Well, here they used a sandwich of 8mm of rubber between two 2mm thick mild steel plates. In the first document, they used a sandwich of 5mm of rubber between two 3mm thick sheets of Domex Protect 300, which is ballistic grade steel with a hardness of 300 BHN, much tougher and harder than mild steel, which has a hardness of only 145 BHN. Both examples were set at an obliquity of 60 degrees. This shows us that even though shaped charge jets achieve penetration by hydrodynamic interaction whereby both the jet and the target behave as fluids, the strength of the bulging plates still matters, and that hydrodynamic penetration is not a sufficient explanation for the interaction between bulging plates and shaped charge jets.

It is understood, then, that all of the sandwich materials are important, not just the interlayer. The potential reduction in penetration performance for a shaped charge warhead could be as high as 83% using 300 BHN steel sheets for a NERA plate with a 5mm rubber interlayer, because the ability of a bulging plate to effectively disrupt a shaped charge jet depends on the strength and toughness of the plate itself. Plus, a minor reduction in the penetration of the cumulative jet comes from penetrating the thickness of the plates themselves (not dynamic thickness). Now, let's see what the T-72B uses.




How T-72B bulging Armour Works:


The bulging plates in the T-72B work essentially as described above, except that the one plate is much thicker and therefore much more rigid than the other, forcing the thinner plate to bulge. The time taken for the rubber interlayer will be slightly shorter, because the pressure wave from the impact of the shaped charge jet with the thick front plate will energize the rubber interlayer before the jet actually passes through it, and the thick front plate will slow down the jet somewhat before it reaches the interlayer, so the bulging plate can manage to interact with the front part of the jet. The diagram below, taken from the old NII Stali website, shows the passage of the shaped charge jet through the NERA plate in three successive stages.




The first stage shows the shaped charge jet penetrating the front plate, creating a bulge in the rear surface of the plate. The second stage shows the destruction of the rear surface, causing an expansion of the rubber interlayer and the subsequent bulging of the thin rear plate. The third stage shows that by the time the shaped charge jet passes through the rubber interlayer and the thin plate, the thin plate has already begun to move perpendicularly to the front plate.

The unidirectional NERA plate might propel its single bulging plate more violently, since all of the energy absorbed into the inert sandwich layer is used to propel only one plate and not two. Still, the effect of a single bulging plate will be less effective than two plates taken together, because there is one fewer plate to disrupt the cumulative jet. However, this might be compensated by emphasizing more violent expansion in a certain direction, as shown below:




(a) "Backwards moving" means that the plate bulges against the direction of travel of the jet. This is known as an "in retreat" or "head-on" type NERA.
(b) "Forwards moving" means that the plate bulges in the same direction as the direction of travel of the jet. This is known as an "in pursuit" type NERA.


The pictures above are not of an actual simulation of cumulative jet hitting a NERA panel. The plates pictured were moved by explosives which were detonated before the jet reached the plate, but they achieve the same effect in its essence. The photos above shed light on an extremely important phenomenon, which is integral to the operation of the armour of the T-72B. In the turret, the NERA panels are all of the "in pursuit" type. This maximizes their performance, effectively reversing any penalties potentially incurred by the unidirectional design, or at least neutralizing the disadvantages.

The reason for the increased effectiveness of in-pursuit plates over head-on plates is explained on page 59 in "Interactions Between High-Velocity Penetrators and Moving Armour Components". Here is the relevant passage:

"The severe scattering of an SC jet is due to instabilities of the same kind as can be found in two fluids in contact moving in parallel with different tangential velocities (Kelvin-Helmholtz instabilities). Although this kind of instability is seldom observed in solid materials, the very high velocity and relatively low material strength of the jet, in combination with the high contact pressure and the motion of the plate allow instabilities to occur in spite of the stabilizing effect of the material strength. It is recognized in fluid mechanics that an accelerating flow is more stable than a decelerating flow, and the negative pressure gradient due to obliquity of a backwards moving plate accelerates the flow in the jet direction while the positive pressure gradient in the case of a forwards moving plate decelerates the flow in the jet direction."





The bulging armour design on the turret of the T-72B cannot be compared directly to its NATO counterparts like the Abrams. The Abrams uses conventional bidirectional bulging plates. Defeat of the tip of the cumulative jet in all cases is achieved by the erosion of the jet against the NERA plate material itself and by relying on the thick steel plate of the main armour. This is not optimum against long rod projectiles, or any KE projectile, really, as thin NERA plates will do very little against such threats and the bulging effects of the NERA armour will only do so much to the projectile before it impacts the main armour. Therefore, we can say that the NERA armour in the Abrams is capable of handling kinetic energy threats, but it is optimized for shaped charges. Given that all of the APFSDS rounds employed by Soviet tanks before the advent of Vant were of a composite design with a tungsten carbide slug, the NERA armour of the Abrams should be sufficient for its purpose. Indeed, the original requirements for the M1 Abrams were to stop 115mm APFSDS rounds at 800 meters. This was not a very high bar to pass, seeing as the T-64A turret from 1967 could have done the same.


The NERA plates have thick, high hardness steel front plates acting as spaced armour (in the same manner as the glacis array, which we have already discussed) working with bulging plates to defeat the projectile before it reaches the main armour, which is itself additionally reinforced. The substitution of bidirectional bulging plates for a unidirectional bulging plate with a thick armour plate could be a deliberate compromise to boost protection from KE threats, but having a thick plate in front of a bulging plate also improves the performance of the bulging plate, as we will later see.


NERA armour can work with both both long rod projectiles and shaped charge jets, but the mechanism of defeat is not exactly the same.

When faced with shaped charges, the bulging armour works in the same way as typical NERA plates. As the first bulging plate bulges, the midsection of the jet (the tip is far too fast to be affected) are put under lateral stresses, thus interrupting its shape. Disruption of the flow of the jet causes it to disintegrate into individual particles, and the disruption of the flow also results in Kelvin-Helmholtz instabilities forming in the jet. A sample of the NERA plates used in the T-72B turret can be seen doing exactly this in the X-ray photograph below, taken from btvt.info. The plate is angled at 68 degrees. 




We can see that large disrupted portions in the jet, like troughs in a sine graph, appear quite often down the length of a jet, indicating the the jet is highly disrupted. It is unfortunate that the photo is so closely focused on the NERA plate, because we cannot see the tip of the jet and its length and condition - that is the most important observation we could make from an X-ray photo like this. Besides that, it is quite clear that the disturbances in the jet only appear after travelling a certain distance behind the bulging plate, which is completely consistent with Dr. Held's findings in "Disturbance of Shaped Charge Jets by Bulging Armour". Interestingly, we can see the base of the cumulative jet at the far left of the photo, indicating that the shaped charge was detonated at a relatively short standoff distance. Overall, it would appear that the NERA configuration was successful, but we must take into consideration that the plate is oriented at 68 degrees obliquity, and this is somewhat steeper than most experimental samples demonstrated in the research papers cited, not to mention the fact that the NERA plates are angled at only 55° degrees in the T-72B turret.


However, this does not mean that the armour in the T-72B turret is ineffective. There are a variety of factors that vastly increase the performance of the NERA plates. As mentioned before, the unidirectional bulging plate of the T-72B NERA can be highly beneficial. The research paper "Study on Rubber Composite Armor Anti-Shaped Charge Jet Penetration" examines the effects of interlayer thickness in bulging armour with a rubber interlayer. It is stated on page 701 that "The interference between the back plate and the jet was neglected because the B plate gave a relatively smooth deflection of the jet without characteristic instabilities, whereas the jet was severely scattered by the F plate". The authors defined the back plate as the front bulging plate, and the front plate as the rear bulging plate. See the diagram below, taken from page 696.





The paper "Shaped Charge Optimisation against Bulging Targets" authored by Dr. Held shows that as the velocity of a shaped charge jet tip decreases, the effectiveness of bulging armour increases. This is succinctly illustrated in the diagrams below.

The velocity of the shaped charge jets was adjusted by varying the thickness of the shaped charge liner without changing the the diameter or the cone angle, which remain at 96mm and 60° respectively. The target was a 10mm steel plate in front of a 2/15/4 bulging armour plate. Shaped charges with liner thicknesses of 1mm, 2mm, 3mm and 4mm were tested. As the thickness of the shape charge liner increases, the lower the jet tip velocity. Jet tip dimeter, however, was unaffected. All warheads were detonated at a standoff of 2 CDs, except for the 2mm liner warhead, which was detonated at 6 CD. This skewed the results slightly, but the trend is very clear:




The shaped charges consistently exhibited more symptoms of disturbance as the liner thickness increases, except for the 2mm liner, but again, this exception exists only because the warhead was detonated at a greater standoff distance so that it attained higher velocity by stretching. The 2mm liner jet was also observed to be thinner than the other three, all of which had the same diameter despite having different liner thicknesses, but this was attributed once again to the increased standoff distance of the 2mm liner shaped charge.




Reducing the velocity of shaped charge jets greatly degrades its performance against bulging armour. The jet tip velocities and the liner thicknesses are given on page 368 in the graph. They are as follows:


Liner thickness, mmJet tip velocity, km/s
19.3
28.9
37.6
46.6


This is relevant to the T-72B because the thick steel armour in front of the turret cheek cavities will slow down a shaped charge jet drastically as it is penetrated, and thus improve the performance of the NERA plates by the time the jet emerges from the back of the turret cheek and into the cavity. While the bulging armour used in the test is not directly equivalent to the bulging armour configuration of the T-72B, these results are still perfectly applicable since all bulging armour designs work on the same basic principles.


The design of the bulging plates in the T-72B have another advantage because of its thick steel plate. A typical NERA array with multiple thin plates would easily reduce the penetration of a small shaped charge to nearly nothing by the time it reaches the main armour at the very back, but the tip of the cumulative jet will pass through each and every NERA plate on its way there, since it is too fast to be affected by any one of the NERA plates, and the NERA plates themselves offer too little resistance, since they are (usually) made from some plastic or elastomer sandwiched between two thin metal sheets. Because of this, there will be a hole in the second plate, third plate, fourth plate and every other plate behind it all the way to the main armour if attacked by a serious large caliber anti-tank missile. This would presumably make the NERA array of an early M1 Abrams highly vulnerable to tandem warheads.

Some tandem warheads have precursor shaped charge with a shallow cone angle like the type found in the PG-7VR, Panzerfaust 3-T, and in many other designs, including guided missiles like the Kombat. The precursor shaped charge in a tandem warhead would simply fail to penetrate all the way through, or not penetrate much at all in the case of tandem warheads that work on the principle of bypassing the reactive armour rather than destroying it. Case in point: patents for tandem warheads like Patent US5415105 A by Dynamit Nobel Aktiengesellschaft (manufacturer of Pzf. 3-T) have outright stated that:

"When firing against ERA-boxes, such boxes were penetrated by the preliminary charge so that the jet from the main charge could flow almost undisturbed through the hole in the box generated by the preliminary charge."

And the Dynamit Nobel official website says this about the Panzerfaust 3-T:

"The warhead of the Pzf 3-T is designed in such a way that the first of both shaped charges immediately penetrates the add-on armour without initiating the explosive contained therein. Less than one millisecond later, the main charge of the tandem warhead ignites and thereby immobilises the vehicle. The shooter therefore is not exposed to fragments thrown back from a reactive protection element."


In such tandem warhead designs, a hole is created without detonation of the ERA block due to the low energy of the shaped charge jet, owing to the shallow cone angle of the precursor warhead which produces a large diameter, low velocity jet. A large diameter, low velocity jet has less energy and spreads the force of impact more widely over the ERA block, thus preventing its detonation. There are proposals to use non-metal shaped charge liners to further enhance this quality, but it appears that copper or brass liners for precursor warheads are still the norm.

Besides this, other tandem warheads may have a high penetration precursor shaped charge. Such designs may protect the primary shaped charge from being damaged by the flyer plates of the ERA block by extending the delay of the detonation of the primary shaped charge so that the flyer plates have flown clear of the path of the primary shaped charge jet. This is described in detail in Russian Patent 2062439. The TOW-2A, for example, relies on detonating the ERA block to clear a path for the primary warhead, as you can see by the high angle liner for the precursor shaped charge in the diagram below (from official U.S government document, acquired by armamentresearch).




In any case, the thick front wall of the turret cavities of the T-72B turret protects the NERA array within from the influence of tandem warheads, though the same cannot be said of any externally mounted reactive armour blocks.


Also, recall that there are diminishing returns when multiple NERA plates are installed in an armour array, so it may not be advantageous to install 6, 7 or 8 NERA plates in a composite armour array but place a relatively thin main armour plate behind it. Such an array would be incredibly effective against individual shaped charges of all sizes, but incredibly ineffective against a KE penetrator.


Besides the effects of bulging armour, we must also not ignore the fact that the thick 21mm front plates make a substantial contribute as both spaced armour and to aid in increasing the effectiveness of the bulging plate by decreasing the jet tip velocity. Reading "Spaced Armor Effects on Shaped Charge Jet Penetration" by researchers from the Nanjing University of Science and Technology, we learn that the space in spaced armour may actually increase the penetration of the shaped charge jet if the air gap corresponds to the optimal stand off distance of the shaped charge. Beyond such unlucky coincidences, increasing the size of the air gap is not as beneficial as compared to increases in the thickness of the spaced plates.


Here is the conclusion of the paper, verbatim:

(DOP = Depth Of Penetration)

"The effect of the distance and plate thickness of spaced armor on penetration was analyzed. For a spaced armor plate with a given size, DOP decreased with the increase in the distance between the first and second plate. However, within a certain stand-off range, DOP did not decrease with an increase in distance mainly because of jet stretch, which created increasing penetration on the penetration vs. stand-off curve. When the distance was constant, DOP decreased with an increase in spaced armor plate thickness."


The paper also details the changing physical condition of the shaped charge jet as it impacts and exits the spaced plates. It is noted that "During the process of target perforation, the jet was compressed, which increased the jet tip diameter. Upon leaving the first target plate, relief of the compressed material occurred, which led to further expansion of the jet tip". Needless to say, an increase in the jet tip diameter and its partial particulation are not very beneficial to the penetration power of the shaped charge jet, but not only that; as noted beforehand, Dr. Held's research showed that "robust" jets with larger diameters but lower velocities performed more poorly against bulging armour.



The RHA plates used in the experiment were 10mm thick, angled at 69 degrees - analogous to the spaced steel plates in the T-72B glacis. The LOS thickness of each plate was therefore 27.9mm (nowhere near the 36.6mm of the plates in the turret). It is stated that the original jet velocity at the point of formation was 6.5 km/s, decreasing to 5.3 km/s as it exited the first plate, further decreasing to 4.8 km/s as it exited the second plate. In other words, the first plate decreased the velocity of the jet by 18.46%, and the second plate by 9.4%. The smaller reduction offered by the second plate is likely due to the stretching of the jet - the first plate was probably not thick enough to particulate the jet and halt stretching. Since we have already established that the heavy front wall of the turret cavity (up to 130mm LOS thickness) will substantially decrease the velocity of a shaped charge jet before it even impacts the thick front wall of the NERA plate, it is clear that the jet will be particulated, slow, and therefore highly vulnerable to the bulging plates in the turret cavity when it finally reaches them.

In addition, the shaped charge jet will most likely be disrupted and particulated as it leaves the first NERA plate, leaving only a section of the jet tip travelling at hypervelocity to continue through the array. The jet tip will probably escape the bulging effect of any subsequent NERA plate past the first or perhaps the second plate in an array of typical NERA sandwiches, but the thick steel wall of the NERA plates in the T-72B turret may reduce the velocity of the jet tip before it impacts the next bulging plate. Reducing the velocity of the jet tip may enable the bulging plate to disrupt the tail part of the jet tip segment, which will probably not result in a big reduction in penetration, but in theory, there should at least be some small contribution. The thick walls also help stop the jet tip by acting as spaced armour.



AGAINST LONG ROD PROJECTILES



NERA works in a similar way against long rod projectiles. In this context, the Soviet style NERA is clearly more suitable than a traditional sandwich configuration, thanks to the heavy front plate if nothing else. One conceivable advantage of the Soviet NERA design is that the heavy front plate enables energy to be transmitted to the rubber interlayer before the projectile impacts the rubber itself, and this may be a major source of energy for the interlayer. Typical NERA sandwiches with plastic interlayers may find themselves neatly perforated without substantial energetic expansion.


The movement of the bulging plates in the T-72B turret may induce lateral movement and produce internal stresses in a long rod penetrator. The addition of a sideways velocity component in a long rod penetrator can lead to yaw.

According to "The Relation between Initial Yaw and Long Rod Projectile Shape after Penetrating an Oblique Thin Plate" authored by Israeli researchers, even one degree of yaw before striking a thin angled plate would significantly reduce that projectile's penetration potential against any armour behind that plate as a result of the deformation of that projectile.




The x-ray photos above show tungsten alloy rods interacting with a sloped armour steel plate with yaw, and no yaw. The rod with no yaw appears to be worse off, as it lost its tip, but that is simply the result of impacting a sloped armour plate (recall the glacis array of the T-72B). The rod with 1 degree of yaw, on the other hand, is seen visibly bent, although it retains its tip. A subsequent impact would show the difference between the two. A bent rod would fail to penetrate as much armour as an intact and straight rod. A combination of the loss of the tip and the bending of the rod would yield the best results, of course, and the combination of sloped spaced armour and NERA in the turret of the T-72B may work in that direction.


The greater the yaw, the greater the negative effect. The hard steel strike plate (45mm) behind the NERA array is angled in the opposite direction to the angle of the NERA panels, so that as the long rod penetrator passes through each panel is becomes increasingly deflecting away (both due to deflection from the bulging plates and due to the natural tendency of long rod penetrators to tunnel inwards into the plate), the relative angle between the rod and the strike plate continually increases. Be reminded that there are at least five bulging modules in the projectile's flight path if the turret is shot head-on. Each individual bulging module works with the next module directly behind it to place the penetrator under great stress, causing it to bend, and perhaps fracture as it passes through the multi-layer array.


According to German tank expert author and lecturer Rolf Hilmes, one method to augment the efficacy of NERA armour against kinetic threats is to incorporate a heavy armour plate in front of the NERA array, so that the penetrator is shattered or fractured before it enters the array. This is the function of the heavy cast steel front plate of the turret cheeks. In later iterations of the T-72B, this effect is augmented by Kontakt-5 reactive armour, so that the NERA array in the turret is highly amplified.


If and when the projectile has gone through all of the NERA panels, it will meet the hardened rolled steel plate backing. Angled at 55 degrees to the horizontal axis, the 45mm plate measures 78.45mm. However, the function of the plate is much more significant than its mere thickness suggests, since the projectile that will be striking it will no longer have an optimal shaping, meaning that this plate could function to totally outright shatter the already fractured and damaged penetrator. The dissimilar hardnesses of the 45mm steel plate and the 90mm cast steel wall behind it turns it into a DHA (Dual Hardness Armour) pairing, making it inherently stronger and more resilient than a single monolithic steel plate of the same thickness. The softer 90mm cast steel wall behind the hard steel plate will also produce less spall. This, in addition to the anti-radiation lining acting as a spall liner, means that the beyond-armour effects of a projectile or a shaped charge would be greatly diminished whether it perforates the armour or not.


Note that bulging armour shouldn't be specially affected by projectiles with impressive length/diameter ratios by any great amount. In fact, it's quite possible that greater length/dimater ratios will actually increase the effectiveness of the array if said projectile is longer but not wider, which would make bending and fracturing it easier, as the stiffness is decreased, while the material properties of the metal remain the same. Snapping of the rod is possible because of the forward momentum of the projectile, which naturally resists a change in the direction of motion. Pressure builds up in the rod due to the large forces opposing each other, and if there is a weakened point in the rod, the thing might fracture or snap. So why continue to increase the L/D ratio of modern tank ammunition? Because the benefit of increased penetration totally offset whatever drawbacks there are.


Also, a rather important point related to the effectiveness of the NERA array in the turret is its ability to perform when hit at abnormal angles, especially considering the regularity in which tanks are hit from the flank. The answer is that the NERA plates would work even better at steeper angles, as it would be if the turret was struck from the side. But that is not to say that the tank is better protected from the side. Not at all; against shaped charges, the array would still have more to lose than gain since fewer bulging modules would be in the path of the shaped charge jet. It is in this situation that the high hardness steel front plates of the NERA plates again become particularly useful as the already good thickness of the plate will further increase due to steeper angling. From an angle of 30 degrees to the side of the turret, a pair of 21mm front plates would measure a total 240mm in thickness, having a relative slope angle of 80 degrees. Also, the high obliquity of the spaced plates at this turret angle ensures high resistance to long rod projectiles. 80 degrees is very close to the critical ricochet angle of long rod projectiles in the 1700 m/s to 1800 m/s velocity range. Since the heavy front wall of the turret cavity will decrease the velocity of an attacking long rod projectile greatly, the angle of the NERA plates will almost certainly be at the critical ricochet angle of the projectile as it comes out the other side of the heavy front wall. See this simulation of a model of 3BM48 "Svinets" interacting with a 50mm hard steel plate at 1600 m/s at an 81 degree slope, with catastrophic results. Also, a long rod penetrator can lose 50% of its penetration power after penetrating a high hardness steel plate of the same thickness as the rod diameter at an angle of 73 to 76 degrees, as we have already learned from our earlier examination of the spaced armour in the upper glacis of the T-72B obr. 1985. Even when not at the critical ricochet angle of a long rod projectile, the very high obliquity of the spaced plates may ensure the immunity of the turret even when fired from the side.

In short, we can say with confidence that the T-72B is essentially impenetrable from a frontal 70-degree arc by contemporary munitions unless the weak gun mantlet was hit.



PROTECTION ESTIMATE



As with all composite and spaced armours, the complex operation of the T-72B's armour does not allow an expression of its protection value in the simple terms of homogeneous RHA plates. However, we can give a good estimate of how it would perform against certain types of munitions on a case by case basis. With Kontakt-1, T-72B is immune to any and all single charge HEAT missiles, and highly resistant against the majority of missiles with tandem warheads. The base armour in the turret cheeks is itself probably capable of taking on a shaped charge with at least 800mm of penetration. TOW-2 and MILAN-2 missiles will be ineffectual against T-72Bs, and it is very likely that the turret will be resistant to TOW-2A and MILAN-2T as well, but only on the thickest parts of the cheeks.


A very basic estimation of the total steel thickness of the turret cheek against shaped charges can be done by adding up the LOS steel thickness of all the plates. First, we add up the 117mm cast front wall (adjusted from 130mm actual thickness) with the 141.2mm cast steel rear wall (adjusted from 157mm actual thickness) and 78.5mm rolled backing plate, and then we add the LOS thicknesses of four 21mm high hardness steel plates, and add four 3mm steel plates to that. If we ignore the disruptive effect of the bulging plates entirely, then the turret cheek should be equivalent to around 503mm RHA against KE and 530mm against HEAT in pure thickness alone. This is reasonably close to the claimed protection value of 550mm against a KE projectile (Tekhnika i Vooruzhenie Magazine, November 2006 issue, p.14), considering that we are simply adding up the thickness in pure steel and ignoring the benefits of the spaced armour configuration and the different hardnesses of the steel plates inside the array. Since jet disruption is the primary mechanism of bulging plates, the actual protection offered by the T-72B turret cheek must be much, much higher than this. Besides that, Kontakt-1 is installed as standard equipment on practically all T-72B tanks, and we know that the reduction in penetration offered by Kontakt-1 at 0 degrees obliquity is 55%, so we can divide 530mm with 55% to get 963.6mm. Adding on the effects of NERA and the spaced armour, the protection value of the turret cheeks must be equivalent to much, much more than 1 meter of RHA steel. Against KE threats, the "more than 550mm" claim is definitely true. It may be more reasonable to guess that the turret should be worth around 600mm of armour steel against a generic long rod tungsten alloy penetrator from the mid-80's, based on the fact that the T-72A turret already achieves a protection level close to 500mm of RHA.  


Both the turret cheeks and the upper glacis armour would be able to handle M833 (1983) very well, as the M833 is less impressive than the M829 but still slightly better than 120mm DM23. For reference, M833 has a 24mm diameter, 427mm long DU penetrator, travelling at 1495 m/s. Seeing as it would have been the most common ammunition available to M60A3 and M1 Abrams tanks prior to the introduction of the M1A1, this is rather important. Latecomers like the M900 (introduction in 1989 to 1990) would still be worse than its more powerful 120mm counterparts like the M829A1, as it travels at a lower velocity (1500 m/s) than the relatively slow M829A1, and it does not have a superior L/D ratio. For reference, the M900 has a 23mm diameter, 603mm long DU penetrator. The penetration of the German DM23 and DM33 tungsten long rod projectiles are completely insufficient, being less than the physical thickness of the steel in the turret array. M829A1 has the best performance among all other 105mm and 120mm tank gun rounds of the time, but it is probably still insufficient at combat ranges.


The turret cheek cavities offer a great deal of modularity and repairability. The bulging armour is simply inserted into the turret cavity panel by panel - as simple as that. In the field, replacing the bulging armour is a simple matter of cutting off the top at the weld lines (very distinctly seen in the picture below), putting new panels in, and replacing the top. This makes battle damage very easy to repair, and it also simplifies the installation of upgraded panels in the future.




Aside from that, it must be noted that despite the huge leap in protection relative to the previous T-72 models, the T-72B's turret remains just as inexpensive. The sheer commodity of steel and rubber makes it very easy and inexpensive to produce the NERA plates of the T-72B, while the workmanship required to process the cast turret does not demand any new skills or any retraining. This is undeniably an important asset during wartime, and would have ensured a very high volume of production even in the hardest times. Indeed, it is worth noting that the peak of T-72 production in Uralvagonzavod was in 1985 - the year the T-72B obr. 1985 entered mass production.



KONTAKT-1




All T-72Bs are outfitted with a set of 227 blocks of Kontakt-1 covering the most of the hull and the forward arc of the turret as well as the turret roof. As mentioned before with the T-72A, each block can reduce the penetrating effects of cumulative jets by an average of 55% at 0 degrees, and by up to 80% when angled at 60 degrees. NII Stali claims that it can reduce the penetration power of a typical anti-tank missile like the Konkurs (130mm diameter) by up to 86%, or 58% for a 125mm HEAT shell, or up to a whopping 92% for low power warheads like the one on the 66mm LAW.


According to NII Stali, the percentage of the tank surface covered by Kontakt-1 is as follows:

Turret Hull Front Hull Sides
62%
82%
32%


The weight of the Kontakt-1 blocks over the three individual surfaces are as follows:


Turret Hull Front Hull Sides
422 kg
288 kg
300 kg


The total weight of the Kontakt-1 set for the T-72B is 1310 kg, 110 kg more than on the T-72A. There are 46 blocks on each sideskirt, 63 blocks on the upper and lower glacis plates, and 72 blocks on the frontal arc of the turret and turret roof.



KONTAKT-5






Kontakt-5 is classified as integrated reactive armour, as opposed to add-on reactive armour like Kontakt-1. Being somewhat heavier and more powerful than Kontakt-1 per block, it was not possible to simply bolt the Kontakt-5 reactive armour panels onto the tank, thus necessitating the installation of the panels onto the base armour by welding. The only way to remove them is to cut off the plates at the weld seams, so it is only possible to remove the panels if the tank is at a depot or if a BREM-1 recovery vehicle is available. If a panel is spent, a new one is simply welded in its place. A complete set of Kontakt-5 weighs 1.5 tons, most of it from the heavy steel plating. A T-72B equipped with Kontakt-5 would weigh around 46 tons dry. A combat-loaded T-72B3 weighs 48.8 tons, according to Uralvagonzavod. NII Stali claims that the total area of the tank protected by Kontakt-5 from a frontal view is 55%. The hull is 45% covered when viewed from a sideways angle of 20 degrees. The turret is 45% covered at a sideways angle of 35 degrees. Atrocious as it may seem, these figures still do not tell the whole story; a large part of the unprotected area is at the turret ring area of the tank, which is the center mass of the tank. While it may have been a novel application for explosive reactive armour, Kontakt-5 was certainly not a panacea.

Although Kontakt-5 is also used on the T-80U, there are actually a few distinct variants of Kontakt-5 that all differ in the exact construction but operate on the same basic unifying principle. The Kontakt-5 reactive armour package used on the T-72B obr. 1989 is unique to the T-72.


There is sufficient information in the public domain for us to simulate the interaction between Kontakt-5 and many modern long rod projectiles. Equipped with the theoretical models designed by Dr. Manfred Held and H.S Yadav, among others, it would be rather simple. However, that is not the aim of this examination. Instead, the aim is to gain an accurate understanding of Kontakt-5, its many intricacies, and the paths taken by Soviet engineers more than 30 years ago.




4S22 EXPLOSIVE ELEMENTS


Kontakt-5 was designed to use 4S22 explosive elements, as opposed to 4S20 which was used in Kontakt-1. 4S22 is an improvement over 4S20 in every way. Chemically, the PVV-12M plastic explosive used in 4S22 is composed of 85% RDX and 15% inert phlegmatizing agent, similar to 4S20. However, 4S22 retains its ductility at a slightly expanded temperature range of -50°C  to +50°C, and 4S22 has a higher flash point of 300°C, making it more resistant to napalm.


The manual for the tank and NII Stali both state that the total number of 4S22 explosive elements installed in the T-72B obr. 1989 is 240 pieces.




According to an NII Stali information placard shared by Alexey Khlopotov, 4S22 is identical to the 4S20 explosive element in dimensions, measuring in at 252x130x10 mm. The mass of the complete explosive element is 1.37 kg, while the mass of the explosive charge alone is 0.28 kg. The PVV-12M explosive charge has a similar composition as PVV-5A but is denser and more powerful. PVV-12M has a density of 1.5 g/cc and a detonation velocity of 7.76 km/s. Because PVV-12M has a higher detonation velocity compared to PVV-5A and a bigger mass, 4S22 has an explosive power equivalent to 0.33 kg of TNT. The thickness of the sandwich layers are assumed to be the same as the 4S20; a pair of 2.3mm steel plates sandwiching a 5.4mm plastic explosive interlayer. Using the Gurney equation for symmetrical sandwiches, the velocity of the plates of the 4S22 element at the moment of detonation should be around 1.258 km/s.


The anti-shaped charge capabilities of 4S22 on its own was demonstrated on a TV Zvezda show called "Военная приемка" ("Military Acceptance"), in episode "Т-90. Бункер на колесах" (T-90: Bunker on Tracks). The screenshot below, taken at the 18:40 mark of the show, shows the experimental set up used for the demonstration. The 60 kg armour plate used as the target is claimed to be equivalent to the steel used in the T-90 tank, and the so-called "dynamic element" is claimed to weigh 1.37 kg, which means that it can only be 4S22. The shaped charge is similar to the one previously used at the 18:17 mark of the show, which was shown to be capable of penetrating around 200mm of the same type of armour plate in LOS thickness. The targets are angled at 60 degrees.




As you can see in the screenshot below, an imprint of the forwards (in-pursuit) flyer plate is left on the armour plate and the penetration of the shaped charge jet is reduced to practically nothing. The fragments of the particulated jet only gouge the plate and crater the surface.




Evidently, a shaped charge with around 200mm of penetration into RHA can reduced to just a few millimeters by 4S22 at a 60 degree obliquity. This is only a demonstration, however, and not necessarily a scientific one. This is definitely not a demonstration of how much Kontakt-5 can reduce the penetration of a shaped charge, as the 4S22 elements are arranged differently in Kontakt-5.



4S23 EXPLOSIVE ELEMENTS



Part of the T-72B3 obr. 2016 modernization involved the replacement of the 4S22 elements in the built-in Kontakt-5 panels with the somewhat newer 4S23 elements originally developed for the Relikt reactive armour system. 




A more detailed examination of 4S23 and its function in Kontakt-5 will be available shortly.



ANATOMY OF KONTAKT-5



Kontakt-5 is much more complex than commonly thought. The typical description of Kontakt-5 paints it as a head-on flyer plate design using a thick and slow flyer plate, and that the design is very inefficient as a consequence. Other descriptions mention the high thickness of the flyer plate as a positive thing, as it would "feed more armour into the path of the penetrator" as it passes through the armour, but we already know that that is largely incorrect. In reality, Kontakt-5 propels a total of three flyer plates head-on towards a projectile in a timed sequence to enable the ERA to resist both shaped charge jets and KE penetrators with minimal compromises.




Dr. Manfred Held conducted exhaustive studies on impact initiation, and his works in this subcategory of ballistics are relevant to us now in our examination of Kontakt-5. It is known that when a projectile or shaped charge jet passes through a barrier placed over an explosive charge, a highly energetic burst of spall and fragments is generated at the back surface of the plate and travels towards the explosive charge, thereby initiating detonation. According to a summary on page 8 in "The Legacy of Manfred Held with Critique", Dr. Held observed that an explosive charge directly in contact with a barrier was less easily initiated by a jet impact than a one with an air gap between the barrier and the charge. One of the explanations is that an explosive charge placed in contact with the barrier is exposed in a smaller area than the charge with an air gap between it and the barrier, as the air gap considerably increases the spall cone angle and therefore the area of the explosive charge exposed to the spray of spall and fragments emerging from the back surface of the barrier. This is supported by a later study titled "High Explosive Initiation Behavior by Shaped Charge Jet Impacts", where it was reported that an explosive charges with a gap between it and the steel barrier will detonate in the impact initiation mode, whereas an explosive charge in contact with the steel barrier detonates in the penetration initiation mode. This essentially means that when an air gap is present, the explosive charge detonates promptly whereas the lack of an air gap requires the shaped charge jet to penetrate far into the charge to initiate detonation. In practical terms, we can safely say that having an air gap decreases the reaction time of Kontakt-5 to shaped charge jets, and thus improves its effectiveness at disrupting the shaped charge jet.

These results apply for both bare explosive charges as well as cased charges (charges encased in a steel container), so it is applicable to 4S22 explosive elements. Russian publications have mentioned that Kontakt-5 relies on this phenomenon to achieve detonation when impacted by long rod penetrators. The explanation is that spall is readily produced when a thin and brittle plate of high hardness is struck by a projectile as well as during the penetration process. This is validated by infamous Russian expert and pessimist Mikhail Rastopshin, a former NII Stali scientist, who revealed in an article penned in 2005 that the flyer plate of Kontakt-5 has a high hardness and is very brittle. According to Rastopshin, this facilitates the generation of spall and fragments upon impact and penetration by a long rod penetrator, thus ensuring reliable and quick detonation of the explosive elements. However, this does not mean that Kontakt-5 relies exclusively on the spall from its heavy flyer plate to initiate its explosive content.

"Test Setup For Instrumented Initiation Tests" by Dr. Held deals with the effects of projectile mass, projectile velocity and barrier thickness on the initiation threshold of encased explosive charges. Held found that adding a barrier in front of the case explosive charge increased the initiation threshold for projectile velocity compared to a plain cased charge, and increasing the thickness of the barrier increased the velocity threshold. This is completely unsurprising, because there is a pressure threshold that needs to be met or exceeded for an explosive charge to detonate, and the spalling and fragmentation of a barrier would transfer only a portion of the energy of a long rod projectile to the explosive charge. The impact of the projectile itself would invariably generate higher pressure for thin long rod projectiles.

This essentially means that the front flyer plate of Kontakt-5 would be detrimental to the reliability of detonation when compared to exposed 4S22 elements. The presence of an air gap in the design of Kontakt-5 would reduce the velocity threshold necessary to initiate detonation due to the increased spall cone angle, but the net effect would still be an increase in the velocity threshold. However, this would not matter if the velocity threshold is within the range of striking velocities for modern APFSDS ammunition. Needless to say, the specific velocity threshold varies between modern long rod projectiles due to the different characteristics of different rounds, so giving a fixed number to represent all long rod penetrators would be misleading. We can only estimate that this threshold encompasses the striking velocities of typical long rod projectiles at combat ranges of 1.5 to 2 km.



In short, if the velocity and mass threshold of the projectile is sufficient, the air gap between the heavy front plate and the explosive elements in each Kontakt-5 module will have the effect of shortening the reaction time of the system against shaped charge jets and facilitates the action of Kontakt-5 against long rod projectiles. For shaped charge jets, the quicker reaction time enables the flyer plates to intercept the tip of the jet and more of the body, thus preventing much of the hypervelocity tip from continuing into the main armour. This explains the very high reduction in shaped charge warhead performance against Kontakt-5 of up to 80% despite having fewer flyer plates and the use of head-on flyer plates rather than a mix of head-on and in-pursuit flyer plates like Kontakt-1. 

The confined nature of the Kontakt-5 panels also improves their chance of detonation for a wider range of shaped charge jet velocities. Held observed that confined explosives have a lower threshold between detonation and reaction and between reaction and no reaction for significantly lower shaped charge jet velocities. The confinement would be partially from the built-in steel case of the 4S22 element itself and from the thick walls of the Kontakt-5 panels. If the velocity threshold for detonation from spall and fragmentation is not attained, the explosive elements can still be initiated by the direct impact of the projectile.

According to "A numerical study on the detonation behaviour of double reactive cassettes by impacts of projectiles with different nose shapes", the detonation of a double stack of explosive cassettes (elements) by high velocity long rod steel penetrators can be prevented by changing the shape of the nose. The paper is highly relevant to our study on Kontakt-5 as the double stack of explosives modeled in the same arrangement as the 4S22 explosive elements in Kontakt-5, and the mechanisms that dictate the initiation of the explosive charge are explained in full. 

Steel rods were used in the simulations detailed in the study. The striking velocity of the rods was 1800 m/s. The explosive elements used in the simulations were roughly analogous to 4S22. The Composition B filler in the explosive elements in the study had a thickness of 7mm, and were encased in steel walls 2mm thick. Needless to say, the Composition B explosive charge used in the study is not directly comparable to PVV-12M, as PVV-12M has a much higher phlegmatizer content and is therefore much less sensitive to impact, but detonating 4S22 elements by direct impact from long rod projectiles is still completely plausible.




The main method of initiating detonation is by shock. The study "The Shock-to-Detonation Transition in Explosives - an Overview" gives a concise explanation of this phenomenon. In short, the impact of an object on the surface of an explosive charge produces a shockwave. The shockwave accelerates deeper into the explosive charge and detonation occurs after the shockwave has travelled a certain depth into the charge, and this depth is called the run distance to detonation. The run-to-detonation differs between explosives, but as a rule, the thickness of the charge must be equal to or greater than the run-distance of the explosive in order for the charge to detonate by this method.




It also found that reducing the velocity of the flat-nosed rod from 1800 m/s to 1700 m/s effectively prevented the initiation of a run-up detonation, but detonation was still achieved from the reflection of the shockwave of impact from the backplate of the explosive element and the build-up of pressure from the compression of the explosive material against the backplate. This effect is undoubtedly reinforced in Kontakt-5 by the placement of the 4S22 elements flush against the surface of the glacis plate, and by the fully contained nature of each Kontakt-5 panel. As detailed in the summary of the paper, the backplate effect is independent of the run-up detonation, and is therefore also independent to the spall effect. It was possible to avoid this effect with hemispherical noses as the build-up of pressure was followed by the displacement of the pressurized explosive material away from the path of the rod, so the pressure was insufficient to initiate detonation. The fact that a small reduction in velocity from 1800 m/s to 1700 m/s was enough to prevent detonation of the Composition B charge by the conventional run-to-detonation method indicates that PVV-12M would most definitely not be initiated even at higher striking velocities due to its low sensitivity. This essentially leaves the shockwave reflection effect solely responsible for initiating Kontakt-5 in the case of a failure to detonate from the spall effect.

There is less unpredictability with shaped charges, as the incredibly high pressure imparted onto an explosive charge upon impact and during penetration by a typical shaped charge jet practically guarantees detonation under any condition. The spall effect from the heavy flyer plate of Kontakt-5 merely reduces the reaction time of the system.


Although Rastopshin is entirely correct in his suggestion that Western long rod projectiles may defeat Kontakt-5 via their relatively low striking velocity, decreasing the velocity of the projectile has a negative effect on its penetration power, and this limits its ability to defeat the base armour. As such, the only viable methods of defeating Kontakt-5 are to have a special tip and to have a segmented penetrator rod. Indeed, modern APFSDS shells fielded by the major leaders in the field - Germany, Israel, U.S.A - are fired at their optimal velocities to maximize their penetrative power, rather than at velocities that are low enough to bypass reactive armour. The best example is the introduction of the Rh 120 L55 cannon in Germany to increase the muzzle velocity of existing 120mm APFSDS ammunition when fired from upgraded Leopard 2 tanks. Even the M829A3 - which is rumoured to be aimed at defeating Kontakt-5 via its low velocity of 1670 m/s - almost certainly has a relatively low muzzle velocity because it is closer to the optimum velocity for its particular alloy of depleted uranium. The graph below, created by Willi Odermatt (a well known scientist specializing in terminal ballistics), shows the relationship between the penetration depth of a generic long rod penetrator for generic alloys of depleted uranium, tungsten alloy and steel. As you can see, the optimum velocity for depleted uranium penetrators is generally lower than tungsten alloy.




From this, it is apparent that the defeat of Kontakt-5 by low velocity impact is currently not being pursued by Western militaries, and is not a feasible solution for the future. Indeed, the renowned German military expert, lecturer and author Rolf Hilmes stated that DM53 has a three-part penetrator and is specially designed to deal with composite and reactive armour, and it is reported that the DM53 is optimized to be fired from the L55 cannon, which allows it to attain a muzzle velocity of 1752 m/s. While this is not the optimum velocity for tungsten alloy long rod penetrators, that is only because the optimum velocity is unattainable with current generation tank guns.


With that in mind, it is clear that the detonation of the explosive elements in Kontakt-5 is not always guaranteed. Special nose shapes on APFSDS projectiles may be able to reduce the pressure exerted on the explosive charge or prohibit the complete detonation of the charge. Russian engineers were fully aware of this fact, as proven by evidence of numerous experiments conducted in the USSR aimed at penetrating explosive elements without detonating them.




During the development of Kontakt-5, Soviet engineers spared no expense to find ways to overcome their own brainchild. According to Rastopshin, experiments have confirmed that long rod projectiles travelling at low velocities do not cause detonation of reactive armour from barrier spall. Another effort was aimed at modifying existing high velocity APFSDS rounds to defeat the armour. One of the successful solutions took the form of a protruding steel probe of small diameter installed on the tip of a specially modified 3BM-22 "Zakolka" shell.




As part of our analysis, we will once again refer to "Test Setup For Instrumented Initiation Tests" by Manfred Held deals with the effects of projectile mass, projectile velocity and barrier thickness on the initiation threshold of encased explosive charges. From his findings, we can surmise that the function of the small steel probe was to avoid the detonation of the explosive elements by presenting a small impact area, whereby the relative mass of the projectile impacting the front plate of the Kontakt-5 panel is minimal, thus preventing detonation from the spall effect. The subsequent detonation of the explosive elements from the direct impact of the rod itself might be prevented by the change in the shape of the armour piercing cap from the interaction of the steel probe. The stresses experienced by the soft armour piercing cap could presumably change its shape from a frustum to a shallow ogive or some other shape that was incompatible with the detonation of 4S22 elements.


As the double stack of 4S22 explosive elements is pinned to the backplate of the reactive armour module, a reliable detonation of the explosive elements should be expected from a long rod projectiles with flat noses. Examples of such projectiles include the 3BM-32 "Vant", 3BM-42 "Mango", DM13 (120), DM23 (120), DM33 (120), DM23 (105), DM33 (105) and many more, including older projectiles. Information on the behaviour of projectiles with stepped tips like the M111 and the M829A2 is not easily found in the public domain, but it is known that stepped tips are used to dampen the shockwave travelling down the rod at the moment of impact to reduce the severity of the damage to the rod.

From what we now understand of Kontakt-5 and the methods of overcoming it, it should be immensely clear that there are no modern long rod projectiles currently in use that are aimed at defeating Kontakt-5 by low velocity or by low contact area, and this generalization includes some of the most modern ammunition such as M829A3 and DM53. M829A3 overcomes Kontakt-5 via a two-part segmented penetrator with a steel segment at the tip, and DM53 overcomes Kontakt-5 via a segmented penetrator as well, albeit with three-parts. It should also be clear now that the M829A2 has no special provision for defeating Kontakt-5, despite widespread rumours that it was designed as a special countermeasure to Kontakt-5. A simple comparison of muzzle velocities between the four members of the M829 series confirms this. The M829 travels at 1750 m/s at the muzzle, while the M829A1 has a greatly reduced velocity of 1575 m/s, and the M829A3 is only slightly slower at 1555 m/s. The M829A2 had the second highest muzzle velocity at 1675 m/s, behind only the original M829. With the initiation of the reactive armour being all but unavoidable, the objective of M829A2 was to defeat the base armour in spite of the damage taken from the flyer plate of Kontakt-5.



ACTION OF FLYER PLATES



It has been shown by Dr. Manfred Held that the primary mechanism of long rod projectile defeat by heavy reactive armour is the transfer of momentum from the flyer plates to the projectile. The desired effect is the deflection of the projectile from its original direction of travel and in the disruption of the shape of the projectile, whether it be by fracturing it, shattering it, bending it, introducing yaw or by cutting it into fragments. In order to achieve this, a sufficiently thick and heavy flyer plate must be used against the long rod projectile, and the emphasis is on the mass of the flyer plate and not the velocity. 


Kontakt-5 modules on the hull rely solely on the action of head-on flyer plates to defeat attacking projectiles, whereas the modules on the turret and on the side hull are designed to send flyer plates in both directions. We have already examined the peculiarities of forward moving (in-pursuit) and backward moving (head-on) flyer plates, and from what we know, it is quite clear that head-on flyer plates are much less efficient than in-pursuit plates. There are a few general rules of improving the performance of flyer plates; increasing the mass of the plate; increasing the velocity of the plate; and increasing the angle of the plate, and any combination of the three.

The efficiency of the modules on the hull are increased through a combination of all three methods to a certain extent, but not without a few negative consequences. The high angling of the Kontakt-5 modules for the hull is guaranteed by the good 68 degree slope of the upper glacis, so there were no compromises that needed to be made here. However, the heavy flyer plates of the hull modules are conspicuously thicker than the plates on the turret modules, and this led to an increase in the mass of the plates. To accelerate this heavy mass to a high velocity, as many as twelve 4S22 explosive elements are used in each module. The twelve explosive charges have a combined explosive power equivalent to 3.36 kg of TNT. The blast has a small contribution in the reduction of the penetration of a shaped charge jet, of course, but the side effect is that external equipment on the tank may be destroyed or damaged and personnel both inside and outside the tank may suffer injuries. There is even a possibility of a flyer plate impacting the gun barrel under the right conditions, but I digress.


Upon detonation, the thin front plates of the first and second explosive elements are propelled at high velocity head-on against the direction of travel of the jet. Estimating the velocity of the thin flyer plates of the 4S22 elements on their own is straightforward, but predicting the velocity of the heavy flyer plates requires a few more steps, because there is momentum transfer from the thin flyer plates of the 4S22 elements to the heavy plate. A simplified model of Kontakt-5 will be used for our calculations.




Due to the very high velocity of the thin flyer plates of the 4S22 elements, it is assumed that they will fuse to the surface of the heavy flyer plate upon impact, so we can classify it as an inelastic collision. The small gap between the 4S22 elements and the heavy flyer plate enable the thin flyer plates to is inconsequential due to the closed nature of Kontakt-5 panels. This enables us to conveniently add the mass of the thin flyer plates to the mass of the heavy flyer plate without other considerations to determine the final velocity of the heavy plate. This assumption is validated in "Momentum Transfer in Indirect Explosive Drive". The heavy flyer plate will be driven by the expansion of gasses only after it impacted by the thin flyer plates. Due to the conservation of energy, the momentum of the thin flyer plates and the heavy flyer plate cannot be calculated as separate entities and then added together, because there is a finite source of energy. Therefore, the mass of the heavy flyer plate alone cannot be plugged into a Gurney equation to obtain its velocity. We must add the mass of the thin flyer plates to the heavy flyer plate, and treat the resultant final mass as a single entity.


According to Russian academicians and experts, the thickness of the heavy flyer plates is 15mm. This is confirmed by the drawings from the T-72B obr. 1989 technical manual. Beyond that, we can figure out the mass of the heavy flyer plate with minimal guesswork by simply adding up the widths and lengths of the 4S22 elements behind each plate to get the approximate surface area, and then multiply that with the approximate thickness of the heavy flyer plate. The simplest modules to calculate are the modules along the top row on the upper glacis. Since there are six 4S22 elements behind the plate, the plate has a surface area of at least 0.19656 sq.m. There is a small gap between the explosive elements and the partitions onto which the flyer plate is welded, and if we make the assumption that these small details add just under 1 cm to the length and width of the plate, then we can round off the surface area to 0.2 sq.m. Using these figures, we get 23.55 kg.

The mass of the 4S22 thin flyer plates is readily determined by simply subtracting the mass of the explosive charge (0.28 kg) from the total mass of the explosive element (1.37 kg), and then dividing that by two. Six flyer plates gives us 3.27 kg, and another twelve flyer plates gives us 6.54 kg for a total of 9.81 kg. Therefore, the final mass of the heavy flyer plate is 33.36 kg.


The mass of the explosive charge will be 0.28 kg multiplied by twelve, giving us 3.36 kg. This is rather low compared to the final mass of the heavy flyer plate after factoring in the mass of the thin flyer plates. It is explained in "Flyer Plate Motion by Thin Sheet of Explosive" by H.S Yadav that at very low C/M ratio, the calculated velocity of the flyer plates using the Gurney model is at variance with experimental results. This is supported by "Gurney Energy of Explosives: Estimation of the Velocity and Impulse Imparted to Driven Metal", which mentions that the recommended restrictions for the Gurney model is 0.2 < M/C < 10 (p. 11). Fortunately, the M/C ratio of the final mass of the heavy flyer plate to the explosive charge is 9.92, placing it just within the stated restrictions. Thus, the results from the Gurney model can be considered reasonably accurate.

It is stated on page 11 in "Gurney Energy of Explosives: Estimation of the Velocity and Impulse Imparted to Driven Metal" that a small gap between the flyer plate and the explosive charge will result in very little decrease in plate velocity, so for all intents and purposes, we will assume that the heavy flyer plate is in contact with the explosive charge, and this means that the Gurney model is applicable. The loss in plate velocity will be considered negligible, but it will be represented in our calculations by rounding down our result to the nearest ten.


Now that we have ascertained all of our variables, we can use the Gurney equation for an infinitely tamped sandwich in our calculations. The reasoning is that even though the 60mm backing plate (the front plate of the base upper glacis armour) is only four times the thickness of the 15mm heavy flyer plate, the backing plate is affixed to a rigid structure - the hull - and the Kontakt-5 panel only occupies a relatively small area of the upper glacis, so the base armour plate does not experience any acceleration from the blast. Since the velocity of the backing plate would be zero, it has the same behaviour as an infinitely thick tamper plate, and it will be treated as such.

Plugging our figures into the Gurney equation, we get 807.47 m/s. Rounding it down to account for the air gap between the flyer plate and the explosive charge, we get 800 m/s.


Despite our precautions, these are still only approximations. The Gurney model used for this calculation is for an unenclosed explosive charge, so the true velocity of the heavy flyer plate could be slightly higher because no energy is lost from the system. An enclosed system like Kontakt-5 would force all of the propulsive energy of the explosive charge to be focused on the single flyer plate.



THE EFFECT OF KONTAKT-5



Due to the high strength of long rod penetrators compared to shaped charge jets, the interaction between it and the heavy flyer plate of Kontakt-5 is generally not the same. One similarity is that both long rod penetrators and shaped charge jets are only eroded while penetrating the heavy flyer plate prior to the detonation of the explosive charge. During the movement of the flyer plate, the interaction can no longer be described as erosion, so by definition, the notion that reactive armour places "more material in the path of the projectile to penetrate" is immediately demonstrated to be false. Rather, during the stage where the flyer plate moves laterally against the penetrator, whether it be a rod or a shaped charge jet, the interaction is better described as the sliding of the plate against the penetrator. Throughout the sliding action, lateral forces are imparted on the penetrator, and the resistive force cuts a crater into the plate.


The operating mechanism of flyer plates against long rod penetrators is summarized on pages 60-61 in "Interactions Between High-Velocity Penetrators and Moving Armour Components". The effect of heavy reactive armour on a long rod penetrator during the penetration of the front plate and before the detonation of the explosive charge is essentially the same as simple spaced armour.


"KH-instabilities do not occur in the case of an LRP interacting with reactive armour. In this case, the high strength of the projectile material and the low projectile velocity relative to that of an SC jet prevent the generation of instabilities. Instead, the abrupt change in pressure at the exit of the plate gives rise to fracture of the projectile."


So before the explosive charge even reacts, the projectile is fractured as a result of perforating the heavy front plate - or rather, the tip is fractured. The mechanisms of spaced plates has already been examined in the section on the T-72B obr. 1985. Navigate to that section for more information. There is a possibility that the heavy flyer plate may also partially condition the penetrator to facilitate more reliable detonation by blunting the tip. As we have seen from the studies presented earlier, long rod penetrators with a flat tip will detonate explosive elements most consistently; but I digress. The vast majority of the effect of Kontakt-5 comes from the motion of the flyer plate against the penetrator, and the paper clarifies the ramifications of the head-on direction and the thinness of the flyer plate.


"The positive pressure gradient and longer interaction time make forwards moving plates more effective than backwards moving plates. Besides from the direction of motion of the plate, the most significant plate parameter for effectively disturbing the projectile is the thickness. Increased plate thickness results in substantial increases in rotation, translation, bending, length reduction and fragmentation of the projectile.

For fractures to occur in the projectile, the plate velocity has to be relatively high, 300 m/s for a plate thickness of one projectile diameter and 200 m/s for a plate thickness of two projectile diameters (only forwards moving plates). Lower projectile velocity results in longer interaction time which increases the effect of the moving plate on the projectile. The experiments also indicated increased effect at higher projectile velocity which has not been explained in these studies."


As mentioned in the passage, the longer interaction time obtained from a forwards moving (in-pursuit) flyer plate is beneficial and vice versa. Not only is less force imparted on the rod, but less of the rod is affected. For Kontakt-5, this means that only the front part of a long rod penetrator will be affected. For this reason and many others, it is apparent that it is not the most efficient arrangement. It would be more efficient to have a single in-pursuit flyer plate of increased thickness, but this is not feasible for tank armour due to the limited space, and the best compromise would be bi-directional flyer plates, which would be a simple description of Relikt. As such, the focus is on maximizing the effectiveness of the head-on flyer plate used in Kontakt-5.


According to "The Break-up Tendency of Long Rod Projectiles", the ductility of high strength tungsten alloy rods appears to not have much bearing on the bending of the rod from interacting with oblique flyer plates, but brittle high strength rods were unsurprisingly more prone to fracturing or fragmenting than more ductile high strength rods. Also, it is noted in the conclusion of the paper that the tendency for a long rod projectile to shatter increases with the strength, thickness and obliquity of the flyer plate, which is quite obvious, but more interestingly, it is stated that high velocity is beneficial for head-on flyer plates while high velocity is disadvantageous for in-pursuit flyer plates. In addition to that, it is stated that the velocity of the flyer plate and projectile have a bigger influence on the tendency of the projectile to shatter than the other parameters, which includes the thickness of the plate. As a rule, increasing the velocity of the flyer plate is more advantageous than increasing the thickness, but having a thick flyer plate travelling at high velocity would obviously be the best of both worlds. Considering the limitations of the practical application of heavy reactive armour on tanks, the high velocity of the flyer plate of Kontakt-5 appears to be the correct choice.

Although it is considered a heavy flyer plate, the 15mm front plate of Kontakt-5 actually has a rather low thickness when contrasted with the diameter of the long rod projectiles likely to be used against it. Even adding on the thickness of the thin flyer plates of the 4S22 explosive elements, the final thickness is only around 21mm to 22mm thick, which is still slightly less than the diameter of a typical heavy alloy long rod penetrator. Nevertheless, the combination of high velocity (800 m/s) and relatively high thickness would make the flyer plate of Kontakt-5 very effective at bending and fracturing a long rod penetrator. The famous photo below appears to demonstrate the effect of a head-on flyer plate against a long rod penetrator:




The penetrator in the photo was moving from right to left. The fragments appear to be a mix of pieces from the fragmented penetrator and spall from the flyer plate, which seems to be the black blob to the right of the rod. The downward curl of the damaged rod is clear evidence that the plate that intercepted it was travelling head-on towards the plate at an oblique angle, representing the flyer plate of Kontakt-5. It is evident that the plate was propelled independently of the rod and intercepted the rod at a predetermined point where the photograph was taken, so it does not fully represent the mechanism of Kontakt-5 where the penetrator impacts the plate and initiates detonation. The heavy fracturing experienced by the rod in the photograph is probably a consequence of the imperfect tungsten alloys available in the USSR at the time (early 80's).

Beyond fracturing and bending the rod, the interaction also induces yaw into the long rod penetrator. According to "Experimental and Numerical Simulation Analysis of The Impact Process of Structured KE Penetrators Onto Semi-Infinite and Oblique Plate Targets" even 1 degree of yaw can cause a tungsten alloy long rod penetrator to break apart in half after passing through a thick oblique spaced plate. The study is particularly useful for us as it explores the effects of a positive yaw angle on the rod, which is compatible with a scenario where a long rod penetrator passes through Kontakt-5. The heavy flyer plate of Kontakt-5 would impart lateral forces on the rod in an upwards direction, and thus generate positive yaw. However, the oblique plate used in the study was angled at only 60 degrees. It is known that increasing the angle of an oblique plate exacerbates the damage experienced by a yawed long rod penetrator. A long rod penetrator with 1 degree of yaw impacting a thick spaced plate angled at 68 degrees would be highly destructive towards the rod.


The method of defeat against shaped charges is the same as any reactive armour or non-energetic reactive armour (NERA), and that has already been covered in the earlier review of Kontakt-1 and the armour of the T-72B. The efficiency of the Kontakt-5 design is not high against shaped charge jets, but the effectiveness of the system is still quite high by virtue of brute force. As explained before, Kontakt-5 sends three flyer plates head-on towards the shaped charge jet; two thin plates from the casing of the 4S22 explosive elements (one 2.3mm plate and one 4.6mm plate), and the single heavy flyer plate, 15mm thick, but the majority of the effect stems from the heavy flyer plate.


A quantitative analysis of Kontakt-5 has not been done yet, although it is definitely possible to do so now, having been equipped with a full understanding of the mechanisms at play. If any researcher or amateur enthusiast would like to assist me in conducting quantifying the effect of Kontakt-5 on generic heavy alloy long rod penetrators, you are welcome to contact me (see "Contacts" page).


NII Stali claims that the reduction in penetration for subcaliber shells (long rod penetrators) to be equivalent to 250mm RHA, but describing it as a solid figure is both illogical and misleading. All other materials published by NII Stali state instead that Kontakt-5 decreases the penetration of subcaliber shells by 1.2 times. Some publications describe the reactive armour as being able to reduce the penetration of a generic long rod projectile by 20% to 35%. Regardless, all given figures were deliberately left vague, as the actual effect of Kontakt-5 depends on the penetrator in question. Long rod projectiles with a very high L:D ratio will not be affected in the same manner as a short and stubby long rod projectile with a very low L:D ratio, and the strength of the rod in question makes a tremendous difference as well. Penetrators with a composite construction like the American M735 or Soviet 3BM-22 will behave even more differently. A "Tekhnika i Vooruzhenie" (Журнал Техника и Вооружение) article claims that Kontakt-5 reduces the penetrating capability of cumulative jets by a minimum of 50% to a maximum of 80%, while NII Stali claims that Kontakt-5 reduces the penetration of shaped charges by 1.9 to 2 times.



TURRET LAYOUT





Kontakt-5 blocks are mounted in a clamshell layout around the frontal arc of the turret. There are total of 120 4S22 explosive elements installed in the turret, 46 on the upper half and 32 for the lower half. The other 42 explosive elements belong to the ERA blocks on the roof, two elements per block.




There are three different sizes of blocks used for the front of the turret, and the manual gives instructions on how to arrange the 4S22 explosive elements inside each type. All of the blocks have two layers of 4S22 elements arranged crosswise.


  • The most numerous type are the blocks for the lower half of the clam shell; 8 of these square blocks are installed on the turret. Each block contains four 4S22 explosive elements. The first layer of 4S22 is laid into the slot horizontally, and the second layer is laid vertically.
  • The second most numerous type are the blocks for the upper half of the clam shell, marked (1) on the diagram; 7 of these rectangular blocks are installed. Each block contains six 4S22 explosive elements. The first two elements of the first layer are laid vertically, and then another cell is added horizontally on top. The second layer is laid horizontally.
  • The third type is a squarish block - marked (2) on the diagram - for the upper half of the clam shell. There is only one example of the third type on the turret; it's the first block to the left hand side of the cannon. The first layer is laid vertically, and the second layer is laid horizontally.

Unlike the panels on the hull, the Kontakt-5 panels on the turret are bolted onto the turret and not welded. This makes it extremely easy to remove the panels if necessary.




As the photo below shows, the cover plate at the end of each reactive armour panel can be unbolted to remove the explosive elements inside. The explosive elements are typically salvaged from destroyed tanks like the one in the photo below and sold on the black market. Photo from lostarmour.info.





HULL LAYOUT





Kontakt-5 blocks cover a little over two thirds of the upper glacis. There are total of 84 4S22 explosive elements installed on the upper glacis; 48 in the top row of panels and 36 in the bottom row. The top row of panels all have the same rectangular design, housing twelve 4S22 elements each. The panels at the corners of the bottom row have a narrower rectangular design with only eight 4S22 elements each. The two panels at the center of the bottom row have an unusual L-shaped design with ten 4S22 elements each.




The photo below (Photo credit to Bellingcat) shows the Kontakt-5 blocks on the upper glacis of a catastrophically destroyed T-72B3 in Ukraine. The access panels for all eight reactive armour panels have been removed, and you can see the explosive elements within.




And here is a photo of an intact tank.




Inserting explosive elements into the two Kontakt-5 panels at the bottom corners is done by unbolting the cover plate at the bottom, laying the 4S22 elements into a tray and sliding it into the panel, as demonstrated in the two screenshots below (Screenshots taken from RT Documentary show "Tanks: Born in Russia (E9)").




Once filled, the panels are simply bolted shut. A tray is used to make it easier to keep the elements from sliding out while bolting the cover plate back on. The tray has no active role in the design of the reactive armour.




SIDE PANELS





There are three Kontakt-5 panels located on either side of the hull. These are a type of explosive flyer plate. They use the same 4S22 explosive elements as the Kontakt-5 plates on the front hull and turret. The side panels provide coverage for the fighting compartment in a 35 degree frontal arc, as illustrated in the photos below:



The panels are mounted on special brackets bolted to the steel screens over the fenders. It is possible to flip the panels up to access the suspension. To do this, the panels are simply lifted upwards until the hole (shown in red in the photo below) is above the hinge, and then the panels are locked in the upward position by inserting a retaining pin through the hole.




The side panels contain six 4S22 explosive elements. There are three reactive armour panels on each side of the hull, each with six 4S22 explosive elements for a total of 36 elements. Each element is laid flush onto the sheet steel tray, and held in place by rubber studs embedded onto the front plate for spacing. This creates an air gap between the front plate and the explosive elements in the same manner as the Kontakt-5 plates on the front hull and turret. This is illustrated in the diagram below, which has been coloured for easy identification. The areas marked in green denotes steel, while the light blue area is the rubber spacer stud and light red marks the explosive elements.  The rubber stud is marked with a (7), the explosive element is marked with a (6), and the front plate is marked with a (5).




An opened panel can be seen in the photo below. Note the six protruding studs on the front plate, corresponding to the positions of the six 4S22 explosive elements. The strip of empty space down the middle of the sheet steel tray is very obvious in the photo.




It is not clear what the strip of empty space is meant for, but it should have no negative effect on the consistency of detonation if the panel is struck from the frontal arc of the tank, because the spray cone of high energy spall and fragments generated by an impacting long rod projectile or a shaped charge jet should be wide enough to detonate at least one of the explosive elements. The only way for an attacking projectile or warhead to slip through would be if it was fired perpendicular to the side of the tank and struck the panel squarely in the middle, but in that case, the reactive armour panel would have very little effect even if it managed to detonate as some obliquity is required for the flyer plates to be effective. 

Like the reactive armour plates on the front hull and turret, the front plate of the side panels is 15mm thick. The sheet steel backplate is just under 3mm thick. However, the 2.3mm-thick steel casing of the 4S22 explosive elements also contributes to the overall thickness of material present in the panel. Since the elements lie flush to the sheet steel tray, the backplate of the system would have an effective thickness of 5.3mm, and the front plate will have a final thickness of 17.3mm after the explosive elements detonate and the front flyer plate of the explosive elements fuse to the back surface of the front plate of the panel.


It is quite obvious that the side panels are not as powerful as the ones on the hull or even the ones on the turret, despite the fact that the panels on the turret also house up to six 4S22 explosive elements, because the turret panels are of the same thickness (15mm) but are much smaller. This deficiency is not entirely counteracted by the bi-directional design of the side armour panels, as the turret panels are bi-directional as well. Rather, the overall effectiveness of the armour for the sides is heavily dependent on the very large air space between the side panels and the side of the hull. According to figures obtained from the T-72B obr. 1989 technical manual, the perpendicular space between the side of the hull to the end of the side panels is exactly 760mm. After subtracting the approximate thickness of the panel itself, the space should be around 720mm. At a 30 degree obliquity (viewing the side of the hull), the air gap is therefore 1440mm wide between the Kontakt-5 side panels and the side hull armour. 

The large air gap gives ample time and space for a long rod projectile or shaped charge jet to disintegrate before striking the main armour. This is particularly important for long rod projectiles, as the penetrator is given much more time to yaw before it strikes the main armour as compared to the reactive armour panels on the front hull and turret, where a 1-degree yaw would be expected. A heavily yawed long rod penetrator has a greatly enhanced likelihood of shattering on impact with the side hull armour.

More of these side panels can be installed if desired.



ROOF BRICKS



The T-72B obr. 1989 had unique hexagonal Kontakt-5 reactive armour bricks installed on the turret roof. Each brick is mounted directly to the cast steel turret roof on a pair of metal spacers. The bricks sit directly atop the anti-radiation cladding, with no air gap in between. This variant of Kontakt-5 roof armour is only one of several variants, as shown on Andrei Tarasenko's btvt.narod. A steel barrier is installed around the forward perimeter of the roof bricks to provide protection from bullets.

One of the biggest mysteries concerning the T-72B obr. 1989 is why the designers felt the need to use a new design of roof ERA blocks with interlocking geometry that would have allowed the blocks to cover the entire turret without leaving any gaps, yet install so few of the blocks that the turret roof is less covered than the original T-72B with Kontakt-1.


Unlike the Kontakt-5 panels on the rest of the tank, these bricks have an entirely unique design, strongly indicating that they are not meant for the same purpose as the others. The bricks are composed of a front plate and a thin sheet steel tray, into which four alternating layers of inert lining and 4S22 explosive elements are inserted. The diagram below, taken from the manual and modified, shows a cross section of the bricks. The areas marked in green denotes steel, while the areas in light blue mark the inert liners and light red marks the explosive elements.




However, the diagram has a small inaccuracy. The two cropped photos below show that the sheet steel trays are actually very thin. The dimensions of the components illustrated in the diagram clearly do not represent reality, but it is safe to say that the arrangement of the components are accurate.




The cropped photo below confirms that there are no protrusions from the interior surface of the front plate at all.




SYMPATHETIC DETONATION




The cost of this performance is the danger of sympathetic detonations of the neighboring modules. As you can see in the adjacent photo, the top of the welded body blew off. Since there is no hole under that particular panel, it seems like the panel beside it inadvertently set it off, meaning that the partition between the two modules disintegrated under the pressure of the detonation of the first panel. This was long-known issue with ERA in general, and particularly with Kontakt-5 due to the large mass contained in each panel.




Presumably, one of the contributing factors would be poor welds. Perhaps sympathetic detonations could be prevented if the partitions were welded onto the hull by professional welders and not journalists.




Although it has been obsolete for over two decades, Kontakt-5 should be appreciated as a unique and ingenious solution to the problem of powerful long rod projectiles during the mid to late 1980's.




FUEL TANKS AS ARMOUR


Two fuel tanks are located on the two front corners of the hull (flanking the driver), which extend from the nose of the glacis to almost up to the turret ring. These fuel tanks provide a modicum of armour.





Diesel fuel is can act as a form of liquid armour in enclosed spaces. The entry of a high energy shaped charge jet into an enclosed liquid medium at high velocities create a shock wave, which are reflected back into the jet. The shock wave emanates from the tip of the shaped charge jet and reflects off the walls of the fuel tank at a right angle to the original shock front. This is shown in the diagram below, taken from the NII Stali website. Due to the fast forward motion of the tip of the cumulative jet, the reflected wave will intersect with the body of the jet.




The ability of a fuel tank to sustain such an effect hinges on the rigidity of its walls. However, testing has proven that even fuel tanks with thin walls are able to stop a shaped charge jet to a limited extent. The main factor is the energy of the jet; when the energy of the shaped charge jet is high, a powerful shock wave is generated and thicker walls are required to effectively reflect the wave without rupturing. A thin-walled fuel tank will be sufficient for a weak shaped charge jet, or a powerful shaped charge jet given sufficient armour in front of the fuel tank to slow down the jet. Soviet testing of the fuel tanks in the T-34 and the T-54 showed that as long as the residual penetration of the shaped charge jet or armour piercing projectile is low, even thin-walled fuel tanks are able to completely absorb the threat without rupturing or exploding.

It wouldn't be wrong to consider the areas of the hull with fuel tanks underneath them to be essentially immune unless the warhead can overmatch the armour by a factor of more than 100 millimeters of RHA steel, though those same fuel tanks might also be a fire hazard if punctured or compromised. The fuel tanks do not have thick walls, and they are not foam-filled, and according to ex-tankers in Chechnya, they will visibly bulge and swell if penetrated by an RPG, though in those cases they were still strong enough to not burst or leak. In one incident during battles in Grozny, a T-72 was struck from the side by an RPG or SPG warhead in the driver's station. This T-72 did not have Kontakt-1 installed, but the combination of the spaced armour of the side skirt and the properties of the fuel tank managed to stop the cumulative jet from hitting the driver. Therefore, we can quite confidently say that the armour over the driver's station from the side aspect is equivalent to more than 400mm RHAe (with side hull armour and side skirt spacing factored in), which should account for its ability to resist a fairly typical PG-7VS rocket grenade. (Obviously, that is not a definitive value, considering the infinite variety of warheads available). The T-72 in that incident escaped with very minor damage.


In some other cases, like the T-72B obr. 1989 in the photos below, damage to the fuel tank may not produce any fire at all. Here, we see that the tank was pierced on the LFP by either a shaped charge warhead or an APFSDS shell from the front. The penetrator easily passed through the thin armour, passed through the starboard side fuel tank, and if the loosely hanging Kontakt-5 panel on the side of the hull means anything, the penetrator exited out the side. If the damaged Kontakt-5 panel was damaged in a separate incident, then the penetrator must have been stopped by the fuel tank. If it had continued, it would have hit the ammunition.









SMOKESCREEN





The T-72 can either lay its own smokescreen by injecting a fine mist of diesel fuel into the exhaust manifold, or make use of its smoke grenade mortars. The former option is an an ingenious, inexpensive, extremely useful and near-inexhaustible source of anti-IR smoke cover - A little-known fact is that the smoke generated from this method is the temperature as the exhaust, thereby completely masking the tank's thermal signature. The only shortcoming of this system is the time taken to envelop the tank. A large number of battlefield maneuvers revolve around the use of this method of smoke generation for concealment.

  
Low volume smokescreen while idling

High volume smokescreen while moving
  
But aside from this, the T-72 also features the Tucha smoke grenade system. It can launch two types of caseless grenades; the 3D6 and the 3D17. They take advantage of a high-low propulsion system much like 40mm VOG series of grenades to launch them out of their tubes at a relatively low velocity. Twelve grenades are available.

Earlier T-72 versions had their smoke grenades installed on the turret cheeks.




This wasn't the wisest idea, since a direct hit on the turret cheeks could potentially remove half the tank of its ability to react by deploying a smoke screen. 




3D6



The 3D6 smoke grenade emits "normal" smoke that can only obscure the tank in the visual spectrum. This type of grenade has been rendered next to useless with the gaining popularity of thermal imaging sights in the mid-80's, now long supplanted by the 3D17 model. It is of the slow-burning type, emitting smoke from the ground-up. It travels anywhere from 200m to 350m after launch, and it takes between 7 to 12 seconds to produce a complete smokescreen 10m to 30m in width and 3m to 10m in height, depending on various environmental factors like wind speed, humidity, altitude, etc. This is not including the time taken from launch to the grenade actually hitting the ground. This is in accordance with frontal assault tactics where tanks advance and maneuver behind a continual wall of smoke generated every forward 300m until they literally overrun enemy positions. The smokescreen can last as long as 2 minutes, depending on environmental factors.






3D17



The 3D17 is an advanced IR-blocking aerosol smoke grenade. It completely obturates the passage of IR signatures or IR-based light as well as light in the visible spectrum. It is effective at concealment from FLIR sights and cameras as well as at blocking and scattering laser beams for tank rangefinders and laser-homing missiles. Unlike the 3D6, the 3D17 grenade detonates just 1 seconds after launch, allowing it to produce a complete smoke barrier in 3 seconds flat. The drawback to this is that the lingering time of the smokescreen is only about 20 seconds, depending on environmental factors. This is enough for the tank to hastily shift its position, but not much more. This grenade detonates 50m away from the tank.
 



NAKIDKA


Nakidka is a type of multi-wavelength infrared suppressant camouflage developed in 1971. Contrary to popular belief, the Soviet concept of warfare was centered around "deep battle" (rather than Zerg rushing), which greatly depended on "maskirovka" - the element of camouflage and deception. Implementation of "maskirovka" includes decoys, stealthy operations, concealment and surprise attacks. Nakidka plays an important role in this. It is a textile "dress" for the tank, which can neutralize the tank's IR signature (except at its exhaust outlet) and reduce its radar cross-section in addition to presenting a totally non-reflective camouflaged surface, thus drastically reducing the tank's likelihood of being detected in the visual and non-visual spectrums.

Nakidka is resistant to napalm and is unaffected by machine gun fire, though it is possible to destroy it with high-explosives. Still, the point of Nakidka is to prevent the tank from being spotted in the first place. It holds up fine against indiscriminate area weapons. A full suit of Nakidka only adds several dozens of kilograms to the tank's overall weight.



ESCAPE HATCH


Like many tanks of the era, the T-72 has an escape hatch. The (rather small) hatch is located directly behind the driver's seat, and therefore most easily accessible by him. The gunner and commander can get to the hatch as well, but they have to be very, very flexible in order to do so unless the turret is traversed to the rear. Nevertheless, it is indispensable in certain situations, allowing crew members to escape the tank if it is flipped over or when the tank is under fire from dismounted infantry. The escape hatch cannot be used while the crew are wearing winter clothing or a bulky IP-5 rebreather. The hatch is strong enough that it does not compromise the integrity of the hull against a 6kg to 10kg anti-tank blast mine detonated under the tracks.




The hatch is far too small for anyone wearing winter clothes, and more rotund tankers will obviously find it impossible to exit through it. The hatch is fully air-tight, and drops out to open. The hatch is as thick as the rest of the hull floor, and is held in very, very firmly in place by four locks.




NBC PROTETCION


Ventilation is controlled from the KUV-11-5-1S ventilation and filtration management box. The ventilation system has a built-in dust ejector at the air inlet to ensure a supply of clean air under normal operating conditions.

The diagram below - taken from "Special Electrical Equipment of the T-72" published by the military department of the Omsk State University of Technology - gives us a cross section of the system. The air outlet for the ventilator in the normal operating mode is marked (21). Air is taken in by the fan, flows through the air booster, and exits through the outlet (21). A dust ejector is installed at the air inlet to ensure that clean air is supplied into the crew compartment even under highly dusty conditions.




The ventilator draws air from a port on the hull roof, located just behind the turret ring. Before crossing water obstacles, the ventilation system is deactivated and the air intake is closed to prevent water from entering the fighting compartment and to prevent damage to the electric motor.

The ventilator housing and the white pipe leading to the air intake can be seen tucked away in the rear corner of the fighting compartment in the photo below. The air outlet from the filtration system drum is indicated by a red arrow.




GO-27





Soviet tank designers were very conscious of the dangers of nuclear warfare, especially artillery-fired tactical nukes. The T-72 perfectly reflected their seriousness, featuring the GO-27 NBC protection suite and the KUV-11-6-1S ventilation system with a filtration unit and the capability to generate an overpressure. A radiation lining shielded the occupants from neutrons. The photo above shows the B-1 instrument and control box, the B-2 sensor for gamma radiation detection, and the B-3 power supply unit. 

The dosimeter detects and measures gamma radiation levels. The B-1 instrument and control panel displays the radiation level in rads per hour (rad/h), and is able to measure and display the radiation level in a range between 0.2 to 150 rads per hour. The system has a measurement accuracy of ± 30%. The B-1 instrument and control panel is shown in the photo below. Photo credit to Leonid Varlamov.




The system has different reactions depending on the rate of dosage of radiation. The system is able to react instantaneously to a nuclear detonation (classified as a Type "A" radiation threat) and initiate the necessary protective measures.

  • Type "R": When the tank is exposed to gamma radiation from a radioactively contaminated site and is exposed to a dose rate of 0.85 Rads/h and above, the response time of the system does not exceed 10 seconds.
  • Type "A": In the event that the tank is exposed to a gamma ray flux with a dose rate of 4 Rads/s and, the response time of the system does not exceed 0.1 seconds.
  • Type "O": When biological or chemical contaminants are detected, the response time of the system does not exceed 40 seconds.

The reaction of the system includes visual and audio signals to alert the crew. The above photo of the B-1 instrument and control box shows three coloured incandescent lights marked "O", "P" (R in Cyrillic) and "A". When any one of the threats is reacted upon, the driver is instantly informed of the type of threat by the colour of the light.

Once a Type "A" radiation threat is detected, the system immediately activates the air filtration system and initiates the lock down protocol, which seals every gap exposing the interior of the tank to the outside environment. Gaps such as the co-axial machine gun port are sealed using steel barriers propelled into position by pyrotechnic charges. Due to the immense speed of gamma rays (very close to speed of light) and the quick reaction of the system, the tank will be hermetically sealed by the time the blast wave from the nuclear explosive arrives. This protects the crew from the blast wave itself as well as from exposure to fallout after the initial blast wave.

A Type "R" radiation threat is a much less serious situation. Type "R" threats are detected when the tank is exposed to radiation from an irradiated environment. The long reaction time of the system to this type of threat is offset by the low danger of minor irradiation.

Type "O" threats are airborne biological or chemical threats. The system detects contaminants in the air using a cyclone-based air sampler and analyzer. The air inlet for the sampler and analyzer is depicted in the diagram below. Due to the rather long reaction time, the driver is sometimes obligated to manually switch on the chemical and biological threat protection measures when entering contaminated zones, assuming that the tank is preceded by a forward reconnaissance force that included chemical troops mounted on NBC reconnaissance vehicles like the BRDM-2RKh.




The air inlet is installed just next to the driver's hatch. Photo credit to the T-72.org Facebook page.





The location of the B-2 gamma radiation sensor can be seen in the photo below, taken from the STV Ground website.




The B-3 power supply unit is installed just next to the gear shift:





PKUZ-1A Digitized Protection Suite




The GO-27 system was replaced with the PKUZ-1A in the T-72B3 modernization. The PKUZ-1A was first used in the T-90A, and features improved detection and reaction time to chemical, biological and nuclear threats. The PKUZ-1A analyzes the air outside the tank using an ionizing system.

The system capable of detecting gamma rays with energies ranging from 0.66 to 1.25 MeV. The system is capable of measuring gamma radiation at dose rates of 0.1 to 500 rads/hour, making it somewhat more versatile than the GO-27. In order to measure the true level of radiation outside the tank, the radiation attenuation coefficient of the armour of the tank and the anti-radiation linings is manually inputted at the factory. This improves the accuracy of the system. Like the GO-27 system, PKUZ-1A automatically executes defensive systems and alerts the crew via visual and audio signals when an NBC threat is detected.

The PKUZ-1A system comes with a new instrument and control box. The new control panel fulfills the same function as its predecessor, but is more user friendly. The old ammeter-based radioactivity gauge was replaced by a digital LCD segment display for quicker and more precise readings. The old ammeter gauge display could not give an accurate reading if the tank was moving because the vibrations caused the indicator needle to jump around.

The new control panel can be seen at the right side of the screenshot below.


    



ANTI-RADIATION CLADDING AND LINER


Anti-radiation measures have been among the top priorities regarding crew protection, no less important than solid armour itself, given the nuclear environment that the T-72 was expected to thrive in. In accordance with this requirement, the T-72 has had an interior anti-radiation lining since the very beginning, and the exterior of the tank had an anti-radiation cladding of the same type installed on the turret and on the hull since 1983. The internal liner is called "Podboi", and is around an inch thick. The lining is applied on all internal surfaces of the tank, giving the crew protection in all directions. The top of the autoloader carouse is also covered with this lining, giving the crew protection from radiation from below the tank. The external cladding is called "Nadboi", and adds additional protection to the areas of the tank with thinner armour to compensate for the reduced radiation absorption from the steel.


The liner is composed of borated polyethylene, a type of high density polyethylene infused with boron, woven into fibers and made into sheets, which are then laminated and molded by a resin to fit around the curves of the tank, presumably using a heat gun. According to Anderi Tarasenko, the name of the material is "boron 2EP002". Boron is known to be extremely effective at capturing neutrons thanks to its large absorption cross section, making it suitable for use as radiation shielding. The fibrous construction of the sheets and the lamination process also makes it a suitable spall liner not dissimilar to early flak vests that used woven nylon plates. NII Stali states on their website that as a rule, spall liners are made from aramid (kevlar) or from UHMWPE (Ultra High Molecular Weight Polyethylene). This hints heavily at the dual roles of the anti-radiation lining.

In the photo below, a T-64 sporting the same type of anti-radiation cladding displays the damage dealt by a 122mm HE-F artillery shell. Note the charred chunks of fabric, proving that the cladding is made from textile sheets.




The 1983 model of the T-72A received anti-radiation cladding all around the occupied regions of the turret. It is around an inch thick in most places, including the turret cladding, most of the turret's interior, the side hull exterior, the hull's interior and most of the hatches. The lining for the driver's hatch is 20mm thick. T-72Bs received this cladding almost immediately after introduction, and are never seen without it.




The circles with four holes that pockmark the surface of the cladding are simply retainers to hold the cladding in place. When the lining is burnt away, these retainers remain. See the photos below (credit to armour-kiev-ua).





The hatches on the turret are covered in a set of specially moulded cladding. The thickness of the cladding is most obvious on the commander's hatch, seen in the photo below.




The shell casing stub ejection port is heavily covered both inside and outside with the anti-radiation material:




As mentioned before, the lining and cladding not only function as neutron absorbers, but they perform admirably as a form of spall liner as well. According to Swedish trials of purchased ex-East German T-72M1s, it was concluded that the anti-radiation liner was perfectly capable of absorbing secondary fragments of penetrating cumulative jets, not only spall. Spall liners, depending on their efficacy, may reduce the spray cone angle of secondary fragments from a HEAT warhead by up to 50% or more if the armour is greatly overmatched, and it is possible reduce secondary fragments by up to 80%. If the armour is not physically perforated, the spall liner may absorb all of the spall. The anti-radiation lining and cladding should have good performance due to its substantial thickness both inside and outside. In fact, this feature has helped to saved lives in at least one incident:

 


In this instance, the T-72 was hit in the flank by an RPG attack which also blew off a part of the port side storage bins. The crew survived and the tank only suffered from a minor puncture wound. It is interesting to note that that part of the tank is above the autoloader carousel, but loose ammunition is stowed on the wall with clips. The survival and quick repair of the tank indicates that there was no ammunition stowed in that particular area. Note that the exterior of the side hull over the fenders is also covered with the anti-radiation cladding.

The presence of the lining is a huge factor in the safety of the carousel ammunition in case of armour perforation, especially from the side, but that's not all; due to boron's large surface area-volume ratio, it does quite well at absorbing blast waves, thus mitigating some of the effects of blast damage. Additionally, the lining helps to insulate the tank and prevents condensation. This helps preserve the myriad of electric and electronic components in the tank.

However, the material does not come without some risks. It is flammable, and constitutes a minor fire hazard. The lining and cladding was partially removed in the T-72B3, as you can see in the photos below.








FIREFIGHTING


To prevent the spreading of internal fires in the engine and crew compartments, the 3ETs11-2 quick-acting firefighting system was installed. There are a total of 15 TD-1 analog thermal sensors installed inside the tank, strategically placed in the engine compartment and crew compartment. The fire fighting system reacts regionally when a temperature difference of at least 150°C is detected in the crew compartment or engine compartment. 

The TD-1 thermal sensor has a maximum response time of 50 milliseconds The reaction time does not exceed 10 seconds, meaning that it takes a maximum of 10 seconds between detecting the fire to the activation of the fire extinguishing system. The sensors do not guarantee reliable detection of fires in the 60°C to 150°C range of temperature differences due to insufficient contrast. This is due to the hardware limitations of the TD-1 sensors.

The driver can manually activate the fire extinguishers wired to the automatic firefighting system from a red control panel to his right.There is also an additional manual fire extinguisher to the driver's left foot.

A TD-1 thermal sensor is shown below.



The photo below shows a T-72A tank. Notice the large number of TD-1 sensors placed on the walls and around the floor. Note that the sensors are all concentrated near potential fire hazards; the conformal fuel tanks, loose ammunition stowage positions, and the powerful amplidyne amplifier for the turret traverse motor. There are five TD-1 sensors placed next to the rear conformal fuel tank alone.





The P11-5 control and information panel is part of the firefighting system. The panel has seven indicator lights. The three lights on the top row (3, 5, 6) are to inform the driver of the serviceability of the pyrotechnic fire extinguisher quick release valves, the light on the center left (2) indicates the presence of a fire in the fighting compartment, the light on the center (4) indicates the presence of a fire in the engine compartment, the light on the center right (7) indicates the status of the air filtration system, and the light at the bottom center (12) indicates if the OPVT mode is activated. By referring to indicator lights (2) and (4), the driver can manually discharge the fire extinguishers for either the fighting compartment or the engine compartment by pressing the buttons (1) and (15), which are located behind a hinged metal cover.




The panel is partially visible at the very top of the photo below (from Prime Portal, credit to Marek Solar).




Like most firefighting systems for armoured vehicles, the 3ETs11-2 uses freon gas as the fire extinguishing agent.




Two handheld OU-2 carbon dioxide fire extinguishers are also provided to supplement the automatic fire extinguisher system. If the TD-1 fire detectors fail to respond (usually in the case of small flames), then these will be the only firefighting tools available to the crew, if the driver opts not to manually activate the extinguishers connected to the 3ETs11-2 system.



The T-72B3 modernization replaced the 3ETs11-2 firefighting system with the newer 3ETs13 "Iney" system.


"Iney" employs a slightly more modern control system, but the fire detection and response algorithms are essentially the same as in the 3ETs11-2. The main improvement offered by "Iney" is the use of new OD-1S optical thermal sensors. Ten of the fifteen TD-1 thermal sensors of the earlier 3ETs11-2 were replaced with OD-1S optical sensors, all installed in the crew compartment to maximize crew survivability. The engine compartment is still only equipped with five TD-1 sensors in the same locations as before.




The response time of the OD-1S optical sensor does not exceed 2 ms. This is a very substantial improvement over the 50 ms response time of TD-1, and contributes towards the much quicker overall reaction time of the system.

The P11-5 control and information panel was replaced with the P708 digital control and information panel. P708 replaces the simple incandescent light bulbs for the indicator lights on the P11-5 with an LED display, which is a much more intuitive way of conveying information to the driver quickly and efficiently, but other than that, the new panel is exactly the same as the P11-5. A close look shows that besides the new LED screen, the buttons, toggles and other interactive components are exactly the same as in the P11-5.




A P708 control panel can be seen tucked away at the right side of the photo below. Photo taken from Popular Mechanics Russia.






ENTRENCHMENT DOZER BLADE




An a self-entrenchment blade is provided at the lower front hull of the tank. It is secured by two rotating latches, which need only to be turned with a wrench by a crew member for the dozer blade to be usable. Needless to say, it is an invaluable tool for self-fortification, allowing the tank to enter hull defilade when natural cover is unavailable, or even augment existing cover with additional concealment.
   

Bolted

Unbolted

With the dozer blade, the T-72 can create a soil barrier in front of itself from even ground in about 20 minutes or more and much less if on uneven ground, but depending on meteorological conditions. On snowed-over terrain, a snowbank may be created in as little as 5 minutes to help conceal the tank.




STORAGE



The T-72 is furnished with a plethora of stowage bins intended for the storage of various things. The most prominent ones are the two large bins located around the rear arc of the turret. These are used for storing the crews' personal effects as well and other accessories. The lids of the bins are sealed by tension latches. These latches are effective at keeping water from entering the compartments.


This is quite the improvement over the T-55 and T-62, as these tanks were not equipped with external stowage bins on the turret. As a result, places to stow day to day necessities was rather limited on these tanks. The Israelis gave their Tiran tanks with Centurian-esque external stowage bins on the turret for this very reason.

The photo below shows the stowage bin at the very rear of the turret. There are two isolated stowage compartments in the bin. One on the right hand side (the left side in the photo) for smaller things, and the central compartment, which is large enough to stow anything you want to. The bin is hinged to the turret, as you can see in the photo below.





The photo below shows the bin hinged open to allow easier access to the engine access panel. How it stays up isn't exactly clear.



Besides the rearmost bin, there is also the side bin. It also has two isolated compartments.




The bins are too thin to deflect bullets or mortar shell fragments.




There is also bank of 4 storage bins on the port side of the hull, directly above the tracks.




The port side storage bins are usually used to store maintenance equipment and spare parts.







MOBILITY


The T-72 followed the T-64 in breaking the mold on the standards of mobility in the face of the need to compromise between the "Big Three": Firepower, Protection and Mobility. The T-72 had the world's most powerful gun, world's best armour, and was also among the world's fastest tanks at the time. Its on and off road performance almost reached the same level attained by the the speed-centric but paper-thin Leopard 1 and AMX-30, outmatched the heavily armoured tottering Chieftain and Challenger tanks and greatly outpaced the sluggish M60A1 and A3, all while weighing and costing less than any of them.
  
The superior engine power of the T-72 and its light weight meant that it could not only traverse difficult terrain, but that it could safely cross low-capacity bridges and make good use of the thousands of tactical bridge layers in Soviet army service, even including the ones derived from the then-already-antiquated T-54. Not only is it possible for the T-72 to exploit light load masonry bridges or pontoon bridges, it is possible for a convoy of T-72s to travel over such structures without needing take turns to drive at a snail's pace.
  
Swedish mobility trials of T-72M1s (and MTLBs) in Northern Norrland between 1992 and 1994 yielded very positive results. The T-72s in question displayed good performance over snow as deep as 0.8m, though it still failed at times to reliably traverse frozen ice banks, but it can be argued that that was because of the inexperience of the Swedish test drivers who might not be too familiar with the idiosyncrasies of the T-72.



ENGINES



The T-72 has been host to several engines over the years, starting with the V-46, evolving into the V-84, and finally the V-92. All of the T-72 engines to date are V-12 four-stroke diesels, with some limited multifuel capability. They are able to consume low octane gasoline (A-66 and A-72), diesel, and jet fuel (T-1, TS-1 and T-2). The driver can set the type of fuel by simply setting a dial located in his station. The engine does not need to be further modified beyond that, but it is highly inefficient when using anything except diesel.

The main method of starting the engine is via an electric starter. In cold weather, the engine can be started with compressed air, or even perhaps by towing. In exceptionally cold weather conditions, the most dependable method of starting is a combination of compressed air and the electric starter. It takes around 20 minutes to start the engine in extremely cold weather, which is much longer than the 3 minutes needed by the GTD-1000T gas turbine engine used on the T-80, but diesel piston engines have their own advantages. Usage of the compressed air starting system is avoided except when absolutely needed as it wears out the engine.






A pair of compressed air bottles are used for the engine starting system. They are placed at the very front of the hull, to the right of the driver's feet but to the left of the right hull fuel tank. The compressed air is also used for the pneumatic periscope cleaning system.



It is not known if the compressed air bottles pose a hazard when the tank armour is struck but not pierced. There is no doubt that the bottles will explode if penetrated by a shaped charge jet or by metal fragments, but the small size of the bottles make that unlikely unless a very specific part of the front hull armour is hit.


V-46-4 / V-46-6

The V-46 liquid-cooled engine is the baseline engine for the T-72 series, first appearing on the T-72 Ural and then the T-72A. It traces its roots to the V-2 which once powered the legendary T-34. True to its remarkable origin, it has a remarkable power density, far above its competitors such as the; MB 837, which powered the Leopard 1 series, AVDS-1790-2A, which powered the M60 tank series, and even the "lightweight" opposed-piston Leyland L60 series, which powered the Chieftain tank. When compared: AVDS-1790-2A - 0.324, MB 837 - 0.426, Leyland L60 - 0.535, V-46 - 0.795, the V-46 comes out on top. Overall, the V-46 and all its descendants are unquestionably robust, dependable engines in every way. A disadvantage of this engine is the amount of smoke it produces, which may expose its position to enemies equipped with thermal imagers.

Output: 780 hp
Rated speed: 2000 rpm
Idle speed: 800 rpm
Fuel Consumption: 1 g / 245 kWh or 1 g / 180hp.h
Torque back up: 9% ... 18%
Weight: 980 kg

T-72 Ural and T-72A power to weight ratio: 18.1 hp/ton


The exhaust port for this engine is characteristically long and narrow. It has very rudimentary sheet steel cooling fins on top. The fins are arranged so that as the tank drives forward, cool air rushes from one side of the fins to the other, drawing away some heat along the way.







The exhaust port connects to the exhaust manifold via a simple duct. The exhaust port is secured onto the duct via a pair of bolts and nuts on either side.






The V-46-4 is the variant which the T-72 Ural uses, while the V-46-6 is used in the T-72A. The only difference between the V-46-4 and the V-46-6 is a change in the placement of oil containersWith the V-46, both the T-72 Ural and T-72A can achieve a top speed of 60 km/h on asphalt, and set an average speed of 35 to 40 km/h on dirt roads.


V-84-1 / V-84MS

 
The V-84 engine differs from its predecessor mainly by an increase in output, along with an insignificant weight gain. The additional power comes from the new centrifugal gear-driven supercharger, which provides better aspiration for cleaner combustion in the cylinders. The increased power offsets the added weight of the tanks that have it installed, which includes the T-72A/B obr. 1984 and all subsequent T-72B models, allowing it to remain as nimble as its predecessors. This engine is much less smoky than the V-46 because the higher oxygen levels in the combustion chamber allowed a greater portion of the fuel particles to be consumed for more efficient consumption of energy, producing more output. One side effect of the added power is the increased heat output. Since the cooling fan for the radiator draws power directly from the engine, the increased heat is mostly eliminated, but more heat escapes from the exhaust manifolds. The engine also wears out slightly faster because of the increased power.




Output: 840 hp 
Rated speed: 2000 rpm
Idle speed: 800 rpm
Fuel Consumption: 247 g/kWh or 182 g/hph
Torque back up: 6% ... 18%
Weight: 1020 kg

T-72B, T-72B1, T-72BA power to weight ratio: 18.87 hp/ton 
T-72B3 power to weight ratio: 18.2 hp/ton 

The exhaust port for the V-84 is identical to the V-46.





Like previous variants, the T-72B has a top speed of 60km/h on asphalt, and an average speed of 35 to 40km/h on dirt roads. This remains mostly unchanged even with the burdensome Kontakt-5 installed. Most T-72B3s are equipped with this engine.



V-92S2F

 
The V-92S2F turbocharged engine boasts an impressive power density of 1.02 hp/kg combined with high standards of reliability. The increased torque reserve greatly improves driving characteristics across rough terrain and the fuel efficiency has been substantially increased, boosting the T-72's already good fuel economy to a new high. The engine is virtually smokeless. The cylinders and pistons were updated and more robust compared to previous engines to cope with the added power.








Output: 1130 hp 
Rated speed: 2000 rpm
Idle speed: 800 rpm
Fuel Consumption: 215 g/kWh or 158 g/hph
Torque back up: 25% ... 30%
Weight: 1100 kg


T-72B3M / T-72B4 power to weight ratio: 21.73 hp/ton

Variants outfitted with the V-92S2F can be identified by the heavily modified exhaust unit, now much narrower, but fatter and with different fins. A new exhaust unit was needed due to the turbocharger.





Without the cooling fins and muffler removed, the exhaust duct itself is just a simple metal tube.







The exhaust duct is fitted over the exhaust manifold on top of the engine, which is oval shaped.





The use of the V-92S2F on the T-72B3M boosts its top speed to a blistering 75 km/h on paved roads and allows it to cruise cross-country at a speed of up to 60 km/h on dirt roads. This elevates the tank's mobility to the level of the T-80BV speed-wise, and gives it something close to parity when moving cross country thanks to the high torque reserve.


The MS-1 cyclone air filter used with all of the V-series engines is adequate for most environments. It is a two-stage filter, and requires a filter change once every 300 km traveled under extremely dusty conditions. According to Sergey Suvorov, the filter requires maintenance every 1000 km in winter, and every 500 km in the summer.


The T-72's engine deck is taken up by the engine access panel, the engine's air intake, radiator/air intake and the cooling system air outlet. All of them except the engine air intake have armoured covers to protect them from bullets and shrapnel coming from above. 





Left and right sides. Engine access panel up front, radiator/air intakes behind it (with armoured covers), and cooling system air outlet behind that (again with armoured covers)

The engine can be easily removed with the help of a 1-ton crane, which can be found at even the most modest depots. In the field, engine replacements are done with the help of engineering vehicles.



Engine access panel hinged open.

However, the T-72's engine is not integrated as part of a powerpack, like on the Leopard 2. Powerpacks are far more convenient to replace. It usually takes more than an hour to replace both the engine and transmission of a T-72, compared with only about 35 minutes or less for more modern vehicles, like the Leopard 2. Highly skilled teams can replace the powerpack of a Leopard 2 in less than 20 minutes.


Air intake for V-46 engine, tucked away discreetly behind the turret


Modified air intake for V-84 engine


The engine deck is cool enough that people can ride on top of it.







COOLING SYSTEM


The liquid cooling system is of a convection type. It works with water and air, used to cool hot coolant oil that is pumped around the engine. The coolant oil first runs up to the radiator unit, where it is cooled by water flowing in a labyrinth of aluminium fins with turbulators, which is itself cooled by flowing air being sucked in by an engine-driven fan at the rear of the engine compartment. The unwanted hot air is pulled into the fan and ejected out of the rearmost outlet in an upwards direction. 





The biggest drawback of this system is that dust particles kicked up into the air from driving at high speed may be sucked up by the high velocity air stream from the cooling fan, thus creating a distinctive "rooster tail" dust cloud behind the tank. It is possible for an observant enemy to detect and distinguish a Nizhny Tagil tank from long distances through this method, as the basic operating principle behind the cooling system is derived directly from the system used in the T-54 and T-62, while the first widespread application of this cooling principle was the T-34. The radiator pack is shown in the photo below.





All reports indicate that this system is slightly limited - sufficient for European climates at best. It was designed so that the engine will work with no loss in efficiency at an ambient temperature of up to 25° C, but the engine will begin to experience very marginal reductions in performance at temperatures exceeding that. Overheating becomes a major issue in ambient temperatures of up to 50° C, which is sometimes recorded at the Thar desert in India. At temperatures above 45° C, the engine will begin to suffer huge reductions in power (up to 33% loss). At such temperatures, the tank must be stopped every 25 kilometers to allow the engine to cool to prevent excessive wearing. The simplest solution, as practiced by most tank crews, is to remove the armoured covers, which helps to improve air intake volume to improve cooling capacity, but this is not sufficient on extremely hot days. At temperatures of 30° C or so, the cooling system is adequate.


Apparently, the V-92 engine series and its accompanying modifications have partially solved the overheating issue. Specific details are not known to the author, but it could only either be an increase in the centrifugal fan's power, or a simple modification of the water flow channels in the radiator, as Indian T-72s and T-90Ss apparently have.
  


Radiator cover removed, exposing the protective louvers within
Cooling system air outlet. Armoured covers for it are removed, but not for the radiator in front of it
  

The photo above shows the engine compartment with cooling pack and engine access panel removed. Note the crossbar to hinge both of the aforementioned accessories. Also note the centrifugal fan at the bottom left corner. It is directly powered by the engine, and thus increases or decreases its power in accordance with the engine's requirements. It is strong enough to throw water out of the engine compartment like a blowhole even while idling.


Centrifugal fan

In the event of damage from air attack or whatever, maintaining or replacing the radiator is quite simple, since the entire unit can be hinged open. The radiator can be disconnected from the coolant pump quite easily, as the two components are only connected by two hoses.




The louvers that protect the radiator inlet, cooling fan outlet and engine air intake can all be shut or opened with the press of a button from the driver's station. Closing these louvers can help protect from attacks coming in various forms, from molotov cocktails to autocannon shells. With the louvers closed and the armoured cover on, the radiator and engine access panel - the largest and most obvious parts of engine deck - can have a very high resistance to hits from air-delivered cannon fire from low angles of attack. Examples include 20x110mm AP-I rounds from A-1 Skyraiders, the USAF's main ground attack plane in the early-mid stages of the Cold War, or 20x102mm AP-I rounds fired from AH-1 Cobras and in many fixed wing aircraft such as the F-4 Phantom and F-16, which may be used ad hoc for the close air support role.





The photo above shows the engine access panel and armoured cover hinged open. Note the spaced armour arrangement. Note the thickness. Since ground attack aircraft and attack helicopters almost never fly at high altitudes to deliver cannon attacks due to the risk of being seen and shot down, the armour is more than enough to deflect hits from all manner of cannon fire. A-10 pilots are trained to approach targets at an angle of attack of around 3 degrees from treetop level. Reducing the obliquity by a few more degrees will not change the fact that the engine deck is too thickly armoured to be affected even by shelling from 30mm DU rounds.





TRANSMISSION



The T-72 uses a hydraulically assisted mechanical syncromesh transmission with dual planetary gearboxes and dual planetary final drives, a type of transmission that is known as a dual transmission system. This type of transmission is principally the same as one from the T-54, but better, of course. It is highly compact, rock solid, extremely reliable (practically unbreakable), and also quite precise, meaning that the driver can direct the tank between obstacles more easilyThere are seven forward gears and one reverse gear. 

According to the manuals for the T-72A and T-72B, the gear speeds (at 2000 RPM) are as follows:

Gears (km/h)

1st: 7.32
2nd: 13:59
3rd: 17.16
4th: 21.47
5th: 29.51
6th: 40.81
7th: 60

R: 4.18


These are assumed to be true until I can find an original T-72 manual.

Results of the tests of Object 172 tanks in the Turkestan Military District in 1968 showed that the average speed of the tanks on a paved road was 43.4 to 48.7 km/h, and the maximum speed recorded was 65 km/h, presumably achieved by driving down a perfectly straight stretch of highway.


The gear shift is much more linear than the one in the T-54.





Here is a GIF of the gear shift of a T-64 being operated. It is identical to the type used in the T-72.





The brakes are of a disc type, hydraulically operated. The T-72 is capable of neutral steering, but it can only turn on a false pivot, meaning that to turn the tank on the spot, one of the two tracks are locked in place while the other drives the tank around it. This system of neutral steering is mechanically simple, but inferior to a true pivot-type steering system where both of the tracks receive power, and one of the tracks is run at the desired speed while the other is run slightly slower in the opposite direction. Besides being slower, false pivot steering creates a huge amount of friction and places more strain on the inactive track, leading to a quicker gradual weakening of the track and a slightly shorter lifespan. As such,it is common practice to release the built-up tension in the track by letting the tank lurch forwards periodically during the turn.

The steering tillers (or levers) are hydraulically assisted, so that steering the T-72 is very light and easy even for an inexperienced driver. The synchromesh gearing system enables the driver to steer the tank smoother than on a  T-54 when he pulls on either one of the tillers, as the changing of gear ratios in the gearbox is smoother with a synchromesh system than with a typical constant mesh system. The synchromesh system is also less harsh on the gears, thus increasing the lifespan on the gearboxes. Driving the T-72 is a very pleasant experience, according to people with firsthand experience. One of the reasons besides the steering system is the low center of gravity of the tank itself. Being so low-slung, turning the tank simply feels better; after all, a double decker bus doesn't turn quite like a lowrider.

Nevertheless, the tiller system is inherently less ergonomic than a steering bar or wheel. The only advantage of the tiller system over the more complex steering bar system is that it is much easier and cheaper to manufacture, and also more durable - durability being a key factor in the decision to stick with tillers. It is no coincidence that the powertrain of the T-72 has a legendary reputation for reliability.


A little-known fact is that with the mud guards on, it is true that the T-72 can only climb vertical obstacles measuring around 0.85m in height. When they are removed, however, the T-72 can scale obstacles at least as tall as 1.2m (already taller than the tracks) or more. The GIF below shows the tank literally climbing straight up a concrete wall.  



(From 1992-1994 Swedish trials in Northern Norrland). Video credit goes to Ren Hanxue from the Swedish Tank Archives blog.



AUXILIARY POWER UNIT


The T-72 can mount an APU, but only the command variants have one. The T-72AK and T-72BK were both equipped with an AB-1 petrol generator, producing 1kW.  





SUSPENSION






The T-72 uses full-length torsion bar suspension. Each wheel has its own torsion bar, which runs across the hull floor and to the other end of the hull. The front two torsion bar-wheel hub interfaces have reinforced bolts, since the T-72 is slightly front heavy and so they will bear the brunt of the tank's weight during forward movement, especially across pot-holed ground.

There are six 750mm roadwheels with three return rollers per each side. The roadwheels are die-cast aluminium alloy, with thick rubberized rims. The wheels weigh 180 kg each. The T-72 Ural used an 8-spoked wheel design, but all subsequent models used a 6-spoked wheel.

The first, second and last roadwheel on both sides are augmented with hydraulic shock absorbers. The front two shock absorbers are highly beneficial as the tank crosses rough terrain, while the rearmost shock absorber is intended to assist recovery when driving through dips and bumps. The shock absorbers are of a rotary type, and are very similar to the ones installed in the T-54.





A cross section of the shock absorber is illustrated below. The device is extremely compact, and is derived from the shock absorbers from the T-54.




The photos below give a good view of the wheels.






 
The T-72 first came with single-pin RMSh tracks measuring 580mm in width. These tracks have rubber bushings that help reduce vibrations and thus, reduce wear and tear as well as noise levels (though still relatively high). A full set weighs just over 1700 kg.




Old drive sprocket

Newer UMSh dual-pin tracks are available, also measuring 580mm in width. UMSh tracks were specially developed for the T-80 due to the high stresses on the suspension due to the high torque from its gas turbine engine and the tank's high average speed across rough terrain. As such, these tracks were the smoothest and most durable of the three types used by the Soviet Union's three main battle tanks. Installation of the newer tracks requires modified drive sprockets, so only the newer modifications of the T-72 have this installed, including some late production T-72B variants. The interior surface of the track pads are rubber-lined so that the rubber rims of the roadwheels roll on a rubber surface rather than a metal one. This prolongs the life of the roadwheels and also helps to reduce the vibrations transmitted to the tank from driving over rough ground. The reduction in vibrations increases the comfort of the crew and improves the accuracy of the weapons while firing on the move. Another benefit of of this track is its ability to be fitted with asphalt-friendly rubber pads. An entire set of tracks weighs just a hair under 1800 kg.





The photo below shows a T-72B3 with UMSh tracks and rubber track pads installed for driving on paved roads. Photo courtesy of Vitaly Kuzmin.





There is a simple mud scraper bolted on to the side of the hull in every T-72, just above the drive sprocket. The scraper helps to prevent loss of traction from excess soil on the tracks, especially sticky mud like clay.







Removing rubber pads on T-90
Throughout the T-72's evolution, it has "fattened up" somewhat, and the largest weight gain was in the T-72B upgrade. While the T-72 Ural and T-72A both weighed 41 and 41.5 tons respectively, the T-72B tipped the scales at 44.5 tons. The T-72B obr. 1989 weighs 46 tons thanks to the installation of Kontakt-5, and Kontakt-1 adds around 1.2 tons.

The T-72 Ural and T-72A exerted 0.83 kg/sq.cm of ground pressure, while the T-72B, being heavier for its thicker and denser armour, put in 0.898 kg/sq.cm of ground pressure. Compared to its immediate foreign counterparts, the T-72 had little to no advantage in soft terrain, despite being a great deal lighter than all of its adversaries. Against the Chieftain, Leopard 1 and M60A1 of its era, the T-72 Ural and T-72A fared slightly better in this respect, but the T-72B was neither better nor worse off than its more modern challengers like the Leopard 2, Challenger 1, M60A3 and the M1 Abrams. The weight discrepancy doesn't manifest in this regard, but it suddenly becomes apparent when we consider the infrastructure of Eastern Europe at the time, especially the bridges - both permanent and temporary ones - which had stricter weight restrictions. Another advantage of the light weight of the T-72 is that it is light enough to be transported on existing rail platforms, and also light enough to be compatible with the weight limit of the old MTU-55 bridge layers and TMM truck-based bridge layers, both of which were and still are present in large numbers in the Russian Army Engineers.  

If the T-72 were to be trapped in swamps, bogs or in extremely deep snow, it may escape with the help of the eponymous log.







By tying the log to track pins on both right and left tracks as illustrated below, the tracks will drag the log along and under them, thus forcing that section of the track to rise above the mud while simultaneously giving the track something more solid to drive over. This allows the tank to get out of the hairiest situations.
 
 


The unditching log was demonstrated in Sweden by an ex-GDR T-72M1 in 1991 as part of a series of tests. Colour photo available on the ointres.se website.





Here is a video (link) demonstrating a tank unditching itself using the log.



WATER OBSTACLES





Like the T-62 and T-54 preceding it, the T-72 is capable of crossing deep water obstacles. Safe fording depths are usually cited to be around 1.2m, but water obstacles measuring up to 1.8m deep may be forded for short distances if necessary. Doing so will require the air intakes to be shut off and the partial implementation of the snorkeling feature (engine draws air from fighting compartment, turret hatches are left open, but snorkel is not installed), since the water level would be above the hull. With the installation of the proprietary OPVT snorkel, fording up to a depth of 5m is possible.  Pre-fording preparations are necessary in order to do so, requiring the edges of all hatches and the openings of various openings and periscopes to be coated with a thick resinous waterproofing paste, as the water pressure at such depths is simply too much for rubber seals to handle. 


The driver must then turn on the bilge pump. It is located to his lower left side.

Crew members are each given a closed-circuit IP-5 rebreather. The crew must put on the IP-5 before entering water as a precautionary measure.





It comprises a watertight, form fitting gas mask, a chemical respirator chamber containing potassium superoxide (KO2), and a flotation collar. The rebreather uses the chemical reaction between potassium superoxide and carbon dioxide, activated by water from the user's breath reduce the former two to oxygen and potassium carbonate. The freshly produced oxygen gas is mixed into the previously exhaled breath to replenish its oxygen content for rebreathing.



IP-5


The OPVT snorkel "breathes" for all three occupants, as well as the engine. In the latter case, an air intake fan duct draws air from the crew compartment and routes it to the engine. The suction effect from the intake fan helps to circulate the air inside the fighting compartment as well. 





The normal NBC-capable ventilation system is inoperable while snorkeling, but this does not mean that the crew is vulnerable to such dangers while snorkeling; recall that the crew must don a closed cycle rebreather system before entering water. This means that the crew never has to breathe contaminated air, although the interior of the tank will be unavoidably contaminated. The OPVT snorkel is installed on the gunner's hatch, through a circular porthole, visible in this picture:



  

Because the hatch can be simply swung open, installing the snorkel is not difficult. The snorkel is fitted with two floating markers during training exercises to indicate the tank's position underwater to help rescue teams locate the tank if it has stopped underwater.


The two photos below shows the snorkel being installed during a river crossing exercise.










Also, the exhaust port must be replaced with a special valve bank to prevent water from entering into the exhaust manifolds.






T-72s equipped with the V-92S2 or V-92SF engines must use different valve units.


All T-72 variants are capable of snorkeling regardless of variant.











ROAD ENDURANCE





All T-72 variants have a total internal fuel capacity of 705 liters, spread across several fuel cells. Two tanks are located on the forward hull on either side of the driver. Another conformal fuel tank is located directly behind the right frontal fuel tank. It also doubles as ammunition racks, and so does the conformal fuel tank directly behind the autoloader, which holds 12 propellant charges. Another 495 liters of fuel is stored in conformal fuel cells located externally on the starboard side fender. The total fuel capacity is 1200 liters.







As you can see in the diagram above, the external and internal fuel systems are not interconnected. They each have their own separate fuel lines, but both connect to the same fuel pump.

Being entirely separated from each other, the driver-mechanic is able to shut off and isolate the internal and external fuel tanks from his station. Isolated fuel tanks will be disconnected from both the fuel pump and the fuel return lines, so the fuel within the tank will be left to sit. This can be beneficial in some circumstances, such as when there is an imminent threat of an internal fire spreading. By shutting off all of the internal fuel tanks, the fuel will not leak out as energetically as it is no longer being drawn by the fuel pump, or maybe even stop leaking entirely, depending on the specific location of the damage to the tanks. It is also possible for the driver to shut off all internal fuel tanks, and rely on external fuel only if the situation allows it. This creates the possibility of filling the internal fuel tanks with water,and since the majority of the volatile propellant charges are stowed in conformal fuel tanks, they can become ad hoc wet stowage racks for increased safety. 




The two externally mounted auxiliary fuel drums each have a 200-liter capacity. These connect directly to the fuel system, and both can be disconnected by the driver at the same time by the push of a button.


The auxiliary fuel tank holders are hinged, and may be folded flush to the hull rear when not in use. 

The T-72 Ural can travel 480km on internal fuel alone, or 700km with external fuel tanks. Thanks to improvements in fuel efficiency on the T-72B3, it can travel 550km on internal fuel alone, or 800km with external fuel tanks despite having the same fuel capacity. As with all automobiles, fuel efficiency decreases while driving cross-country. The amount of engine power needed increases as the harshness of the terrain increases, and so does fuel consumption. 
  
Because of the T-72's relatively large fuel capacity and high fuel efficiency, refueling the T-72 isn't even necessary for short continuous operations (lasting no more than 3 days), and this greatly eases the logistical burden on the frontlines.




DRIVER MECHANIC'S STATION


According to user testimonies compiled by the author, the driver's station can be definitively said to be the most comfortable place to be in the T-72. Anecdotes from people who have sat in the driver's seat have reported that the station is spacious enough to let someone more than six feet tall to operate the pedals with a comfortable allotment of legroom. When driving, the driver must hunch slightly forward in order to operate the steering levers, step on the pedals and look through the periscope at the same time. Besides anecdotal sources, we can once again refer to this diagram from "Human Factors and Scientific Progress in Tank Building" by M.N. Tikhonov and I.D. Kudrin as provided by Peter Samsonov, we can see that the driver of a T-72 gets 0.864 cubic meters of space. That's more than the 0.621 cubic meters afforded to the driver of a T-55. The driver enters and exits his station via an oval 530mm-wide hatch located centrally on the hull axis, underneath the cannon. The driver can only exit the tank when the cannon is elevated or oriented to one side.




The driver is provided with a single forward-facing TNPO-168V periscope to facilitate driving. It is a very wide periscope measuring 267mm across - much wider than the driver's head - with a binocular field of view of 38 degrees, and a total field of view of 138 degrees. The periscope provides 31 degrees of vision vertically - 15 below the horizontal axis and 16 above. The view from the TNPO-168V is superb (reportedly). Szabó István, a non-military Hungarian with extensive experience driving demilitarized tanks, described the TNPO-168V periscope as "so wide that it looks like a small window from inside! Forward visibility is excellent for such a periscope! No complaints here". Like all the other periscopes on the T-72, the TNPO-168V is heated through the RTC heater system.


There is a horizontal handlebar below the periscope. It is not part of the periscope. It is simply a handlebar for the driver to hold on to when shifting in or out of the hatch.

The picture below shows the view from a TNPO-168V. As you can see, forward visibility is very good indeed. It helped that the periscope itself is quite short, meaning that the distance between the eyepiece mirror and the aperture mirror is very short, so the "tunnel effect" is minimized. 





Another good example of the excellent visibility from the TNPO-168V periscope is demonstrated in this video (link).
When not in use, the TNPO-168V periscope is stowed away in its aluminium container.





For night time driving, the driver is provided with a TVNE-4B passive-active binocular periscope with a pair of Gen 2 light intensifier moduleThe periscope runs on the tank's 27V power supply system, and can run continuously for eight hours. It is typically kept in its proprietary aluminium box and stowed away by the driver until it is needed.

The periscope is much narrower than the TNPO-168V, but the TVNE-4B still provides a decent field of vision as well as an acceptable viewing distance. TVNE-4B stands for "Tank Driver's Passive Night Vision Optic, model 4 with built-in power supply". According to "Optical Night Vision Devices For Armoured Vehicles" by S.A. Belyakov and published by the Russian Ministry of Defence, TVNE-4B facilitates a viewing distance of up to 100 m in the passive mode under ambient light conditions of 0.005 lux (moonless, starlit night), and 60 m in the active mode using the FG-125 IR headlight. The active infrared mode of vision is very similar to the M24 active IR periscope, but the passive mode offers inferior range compared to the AN/VVS-2 passive periscope, which offers a viewing distance of 150 m. In terms of overall quality and functionality, the TVNE-4B is closer to the obsolete M24 than the AN/VVS-2. The TVN-5 closely mimicked the AN/VVS-2 and offered better performance, but came much later and is used only in limited numbers, so we will not be examining it in this article.





The periscope can be directly inserted into the periscope slot for the TNPO-168V without any modifications, but a plastic spacer is slipped on top of the aperture head to give it a proper fit and to prevent water and mud from ingressing through the gaps. The plastic spacer can be seen at the very top of the exploded diagram below. The periscope only has a decent horizontal field of view of 36 degrees and a vertical field of view of 33 degrees, but more importantly, the driver has depth perception. Most night vision periscopes have two eyepieces but only a single aperture, so the driver lacks stereoscopic vision and thus lacks depth perception.



Although TVNE-4B only has a 60 meter view range in the active mode using only the hull's single small IR headlight, it may also pick up infrared light from the turret's three IR spotlights. Indeed, the single FG-125 IR light located just beside the auxiliary/night sight on the turret is meant to augment the driver's viewing distance when operating in the active imaging mode and also to provide a source of light when the tank is wading across water obstacles. The periscope has 1.12x magnification. Compared to the AN/VVS-2 passive driver's periscope, the TVNE-4B has poorer performance all across the board, except that it enables stereoscopic vision.


This video shows the image intensifier of the TVNE-4B periscope in use. Here is a screenshot from the video:





From the video, the claimed 100-meter viewing range of the periscope is shown to be valid, and it appears to be more than adequate for nighttime driving. Here is another video of the TVNE-4B in use, this time in a T-90. The IR headlight on the left side of the upper glacis is used for illumination in this instance, and the range of vision seems to be worse, but this could be due to the low video quality (240p).


There is an accessory windshield that may be attached to the outside of the hatch. Its main purpose is to protect the driver from bugs and dust while driving in non combat conditions.





It is not unique to the T-72 in any way. Many other Soviet vehicles can mount these windshields.





The driver enters through a pill-shaped hatch. Two TNPA-65A viewing prisms are embedded in it, one looking in the 10 o'clock and the other in the 1 o'clock direction. Looking through them requires the driver to look upwards. This layout is generally far less convenient than the more commonly encountered bank of three viewing prisms found on the T-80 and Abrams as well as most others. The TNPA-65A periscopes are very narrow, almost slit-like. It is difficult to see very much other than the tracks and part of the road, but it would also be very hard to hit or damage them with machine gun fire. The TNPA-65A periscopes are meant to check the corners of the tank only. They are far too limited for driving during combat.






As mentioned before, the TNPA-65A periscope provides 14 degrees of binocular vision horizontally, and only 6 degrees of vertical vision.






The driver's hatch itself is 20mm thick. The rubber seals make them completely watertight down till a depth of around 1 or 2 (relative to the height of the hatch, not the turret roof). Unfortunately, the seals on the TNPO-168V periscope are not nearly as dependable. Being mostly watertight, the tank can ford streams as deep as 1.2m or deeper without the danger of excessive water ingress.

Steering the tank requires the use of two hydraulically assisted tillers, which are located on either side of the knees of the driver. Though the tiller steering system can be considered one of the more antiquated aspects of the T-72, it's worth noting that many of its rivals like the AMX-30, Chieftain and Challenger used the same system as well. However, most main battle tanks had already grown out of tillers and progressed into steering wheels even by the 1960s, like the M60 and Leopard 1 did. The Leclerc and Leopard 2 both use steering wheels and the Abrams tank uses motorcycle handlebars. The only exception is the Challenger 2, which (shockingly) still retains a tiller system as well.

The driver sits on a bucket type seat, with bolsters on each side. The seat can be adjusted for height in order to accommodate persons of a wider range of height, and also to raise the driver high enough to peek over the hatch. It has been reported to the author that the driver of a T-72 gets quite a lot of legroom, and that it is quite comfortable, more so even than the commander's and gunner's stations.




Like the commander and gunner, the driver's "air conditioning" comes in the form of a DV-3 plastic fan.



All of the driving-related indicator gauges are placed on a board to the driver's left, like in previous tanks like the T-62, T-54 and T-34. The placement isn't exactly convenient, but looking at them while driving (in any tank) isn't really very necessary anyway.





Behind is the left front hull fuel tank. The fire extinguishers for the hull's automated firefighting system is located underneath it. 

Over at his left foot there is a rather rudimentary GPK-59 gyroscopic compass for directional navigation. It is particularly useful when driving underwater when nobody in the tank has any scenery to refer to for a sense of direction. The use of gyrocompasses can perhaps be labeled as a rudimentary form of an Inertial Navigation System (INS), advanced versions of which are often present in modern combat vehicles due to their independence from outside input contrary to a GPS-based navigation system. Sadly, the T-72 has not received either in any of its iterations.





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Bibliography

T-72 Ural Armour Against NATO, Mikhail Baryatinsky
(Михаил Барятинский, Т-72 Уральская броня против НАТО)

https://www.litmir.me/br/?b=544730&p=1


Vehicles and Weapons Magazine, 2006 November issue
(Журнал Техника и Вооружение 2006 год, 11)

http://hobby.rudic.ru/zhurnal-tehnika-i-vooruzhenie


V.A Grigoryan, Tank Armour, 2007(Защита Танков, В.А Григорян 2007)