Each Kontakt-1 block consists of two 4S20 explosive elements which are composed of plastic explosives sandwiched between two flat steel plates. The operating principle of the armour lies in the disruption of shaped charge jets through the violent separation of the steel plates sandwiching the explosive layer upon detonation. 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 at very specific angles. This is examined in the diagram below, taken from the book "Защита Танков" (Protection of Tanks) by V.A Grigoryan. The column of numbers 'N' 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 for a total of three intersections.
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 side skirts. 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 may arise when the blocks are installed at a smaller angles. 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.
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 and the explosive power is equivalent to 280 grams of TNT. The explosive elements are highly insensitive to ensure safety during rough handling first and foremost, but also to ensure that unintended detonation from machine gun fire and napalm attack is not possible. Kontakt-1 is safe enough from external damage that destroyed tanks clad in Kontakt-1 are universally observed to retain their Kontakt-1 blocks even if the metal of the tank itself is completely burnt out from a catastrophic destruction. This shows that the blocks do not detonate even when burned by the intense heat of ammunition or fuel fires for prolonged periods. Here are some examples:
Due to the 68-degree angle of installation 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 reactive armour. The overlap between the blocks when viewed frontally is also sufficient to counteract the decrease in ERA efficiency from edge effects (shaped charge jet impacting the edge of the ERA element).
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 side skirts. 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 may arise when the blocks are installed at a smaller angles. 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.
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 and the explosive power is equivalent to 280 grams of TNT. The explosive elements are highly insensitive to ensure safety during rough handling first and foremost, but also to ensure that unintended detonation from machine gun fire and napalm attack is not possible. Kontakt-1 is safe enough from external damage that destroyed tanks clad in Kontakt-1 are universally observed to retain their Kontakt-1 blocks even if the metal of the tank itself is completely burnt out from a catastrophic destruction. This shows that the blocks do not detonate even when burned by the intense heat of ammunition or fuel fires for prolonged periods. Here are some examples:
The burnt-out Georgian T-72B and T-72AV tanks shown below illustrate this point.
The highly insensitive nature of the plastic explosives contained inside 4S20 explains why Kontakt-1 has practically 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. However, the 4S20 elements may still constitute a fire hazard if the tank is attacked with napalm because the explosive charge will still burn when exposed to intense heat for prolonged periods. This essentially means that large areas of the tank may become unprotected after it is doused in burning napalm.
The weight of each block is 5.7 kg and 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 before putting tanks into long term storage.
The detonation of one Kontakt-1 block generally has little effect on the neighboring blocks due to the sufficient sturdiness of the 3mm sheet steel boxes. This completely prevents chain detonations. However, the sheet steel boxes are generally not enough to resist the blast pressure of a large explosive warhead, especially if there is a strong fragmentation effect. As such, even though an impacting HEAT missile or grenade can only detonate the Kontakt-1 blocks that intersect with the trajectory of the shaped charge jet, the explosion can strip off multiple blocks from the surface of a tank. Energetic fragmentation is also capable of detonating the 4S20 explosive elements in Kontakt-1, which makes powerful tank-fired HEAT shells the most effective at removing the ERA from the surfaces of a tank, as they have thick warhead casings made from steel, as opposed to lightweight aluminium such as on missiles and light grenades. In fact, the fragmentation produced by 125mm 3BK-14M shells have enough energy to pierce the front armour of most APCs.
In the article "Динамическая защита. Израильский щит ковался в... СССР?", it is reported that between 9-31% of the protected surface area of one side of a tank turret may be left unprotected by Kontakt-1 blocks after the detonation of a large shaped charge warhead. The reactive armour blocks on 16-71% (!) of the protected surface area of the upper glacis may be neutralized and the blocks on 31-51% of the protected surface area on the sides of the hull may be neutralized. Testing was done with 9M112M missiles and 3BK-14M shells, both of which contain large explosive fillers. Adding on to that, 3BK-14M has a powerful fragmentation effect which enhances its effectiveness in removing a larger number of Kontakt-1 blocks.
This is further elaborated in the report "Анализ Живучести Динамической Защиты Отечественных Танков" (Analysis of the Durability of the Dynamic Protection of Domestic Tanks). It is reported that on average, the area covered by Kontakt-1 that is left exposed after the impact of a single tank-fired HEAT shell (represented by 125mm 3BK-14M) is 70-85% on the upper and lower glacis of the hull, 20-30% on each side of the turret, and 50-55% on the sides of the hull.
The number of Kontakt-1 blocks removed by the grenade of a light shoulder-fired weapon like the RPG-7, Carl Gustaf or M72 LAW is much smaller by comparison. The photo on the left below shows a T-72B that was struck by a HEAT grenade in the side during combat in Chechnya. A PG-7 grenade of unknown model was used. The combined blast power of the grenade and a single Kontakt-1 block managed to remove a small number of blocks around the point of impact and left a gash in the skirt, but the damage is generally very limited. The photo on the right below shows a Syrian T-72AV that suffered similar damage. The detonation of a single Kontakt-1 block tore a hole in the skirt and removed the other blocks around it.
METHOD OF OPERATION
When a shaped charge jet passes through the explosive elements, the resulting explosions will propel the steel casing 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. This is compounded by the lack of special angled brackets for Blazer to increase the obliquity of the explosive elements.
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 around 2-3mm thick. This relatively high thickness gives the boxes sufficient stiffness so that they can support the weight of a person standing on top without deforming, and sufficient durability so that it cannot be easily destroyed by heavy objects falling on the tank (bricks, concrete) or by small arms fire. The relatively high thickness also helps to guarantee that impacting projectiles experience enough resistance to fuze properly as opposed to penetrating straight through the ERA block without detonating. Besides that, the walls of the steel box do not merely function as a container for the explosive elements but also contribute to the overall disruptive effect against shaped charges when the explosive charge is detonated.
The thicknesses of the three layers of each 4S20 element 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. Other sources state that the sandwich composition is 2-7-2 but this is in contradiction to this information placard that states that the thickness of a 4S20 element is 10mm. Regardless of the exact thicknesses, 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 Rickard O. Lindström.
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 paper "A numerical study on the disturbance of explosive reactive armors to jet penetration" penned by a team of Chinese researchers gives us a detailed look into how Kontakt-1 works. 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 explosive element (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 shown below:
With a V-shaped design, the pair of ERA 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 shaped charge 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) by up to 86%, or by 58% for a 125mm HEAT shell, or up to a whopping 92% for smaller sized warheads like the one on the M72 LAW. These figures are generally consistent with the 90% reduction reported for the Chinese V-shaped ERA at a 68 degree obliquity, with the exception of the claimed reduction of only 58% for a 125mm HEAT shell. 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 around 105mm). A plausible explanation is that the thick-walled spike tip/probe protects the tail of the jet and the copper slug when the reactive armour block is detonated and the flyer plates are propelled into the path of the jet. This presumably reduces the disruptive effect of the armour.
Furthermore, NII Stali claims that Kontakt-1 can reduce the penetration power of a typical anti-tank missile (using the Konkurs as an example) by up to 86%, or by 58% for a 125mm HEAT shell, or up to a whopping 92% for smaller sized warheads like the one on the M72 LAW. These figures are generally consistent with the 90% reduction reported for the Chinese V-shaped ERA at a 68 degree obliquity, with the exception of the claimed reduction of only 58% for a 125mm HEAT shell. 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 around 105mm). A plausible explanation is that the thick-walled spike tip/probe protects the tail of the jet and the copper slug when the reactive armour block is detonated and the flyer plates are propelled into the path of the jet. This presumably reduces the disruptive effect of the armour.
The rationale supporting the design solution of arranging the explosive elements with a V-angle is examined under subheading 5.3. The research shows that the maximum performance of the ERA elements 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 at the optimal angle, to put it mildly, 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 manage to perform its primary function even with an acceptable loss in performance. However, it appears that the specific V-angle of 9 degrees used on Kontakt-1 was largely arbitrary. 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.
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.
During the the First Chechen War, many tanks had their 4S22 explosives stolen and sold on the black market due to the poor economic conditions of Russia at the time and the extremely poor living conditions of Army servicemen. Kontakt-1 bricks were not filled during peacetime for safety reasons. According to protocol, they would only be filled during preparations for a military operation, but many tanks in Chechnya were left empty partially due to the haste of the preparations (hundreds of bricks on each tank makes it a tedious chore) and due to theft. As a result of a combination of these unfortunate circumstances, many tanks rode into Grozny with Kontakt-1 bricks, but with no explosives inside. Similar cases of theft have been reported recently in Ukraine.
It is interesting to note that even empty Kontakt-1 blocks can still offer a modicum of additional protection from light grenades due to the increased size of the air gap, as demonstrated during combat in Grozny. The additional space provided by the empty box itself (70mm) and the air gap between the box and the side skirt (17mm) increases the total size of the air gap from 745mm to around 830mm.
Putting some components that are used on varios tanks on a separate article is a great idea. Thanks
ReplyDeleteDoes one know where an individual could purchase this to put on their bulldozer for non related reasons.
ReplyDeleteIn any random Russian arms depot
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