Date of publication: 15.02.2017 (Authors: Evgeny Chistyakov, Dmitry Kupryunin, Mikhail Alexeev, Alexey Kimayev)
Date of translation: 01.07.2017-02.07.2017
Note: I want to thank for the help in translating @Urich_jr, and also @warsmonitoring for the idea of this translation. Thank you once more, guys!
The effectiveness of additional protection of military vehicles
Armed conflicts in recent years convincingly show that military hardware used in them constantly needs to strengthen protection, while other important parameters - firepower and mobility - are often superfluous. For example, a tank in the city does not need a gluttonous engine with a capacity of 1500-1800 h.p., and the armor-piercing capabilities of the gun required in very rare cases. The problem with the deficit of protection increases many times, when modern weapons and obsolete armored vehicles with a low level of protection are involved in the conflict. These scenarios are mainly happens now.
It should be noted that even in large-scale wars there was always not enough effective protection, and the conflicting parties were looking for any ways and means to strengthen it.
Often, those who directly use military hardware often have to take care of increasing their protection, and the effectiveness of the taken measures is largely determined by their experience and competence. Ever since World War II, bags with sand and construction debris, various gratings and nets, metal sheets, rubber, and so on, have been widely used to increase the protection of combat vehicles.
M113 with additional protection from sandbags, 1982 Lebanon.
T-72 of the Syrian government forces with additional protection made from construction debris, 2014.
BTR-60 of Kurdish militia, equipped with improvised additional protection.
BTR-70 with an additional protection kit manufactured by the Nikolayev diesel locomotive repair factory (Ukraine).
Let's try to evaluate some of these solutions from the standpoint of modern ideas about the interaction of weapons with protection. Most of the upgrades are associated with attempts to protect themselves from cumulative anti-tank grenades, the availability and cheapness of which has made them one of the most common and effective means for fighting with armored vehicles. Let's start with the simplest ways to increase protection - sandbags or bags with construction debris. What such protection can?
Its main purpose is protection against cumulative munition (but they also raise the level of bulletproof protection). We will try to evaluate the anti-cumulative resistance of such protection in the so-called "steel equivalent - L(equivalent)", for which we will use one of the parameters of any protective material - the dimensional coefficient [this translation – “dimensional coefficient”, – I think, is not correct, just word-to-word translation in fact, but I have no idea how to translate it right] Kг = L / L(equivalent). The dimensional coefficient of sand by the cumulative jet is approximately 3.8-4.0, for concrete - 3.5.
Note: The physical meaning of Kг is as follows. If a cumulative jet of some anti-tank grenade can penetrate a steel armored plate with a Lequivalent thickness, then the same grenade can penetrate into another material for a thickness equal to Kг × L(equivalent). For sand, this will be (3.8-4.0)×L(equivalent), for concrete - 3.5×L(equivalent). For other materials, the overall coefficient of Kг will be, respectively, different. This coefficient will be different for other weapons - bullets, debris, armor-piercing projectiles and it is determined experimentally.
Thus, for the cumulative jet a sandbags with 500mm thickness is roughly equivalent to a 125mm thick steel armor, and 140mm of construction debris based on concrete.
It can be said that this is enough high additional level of protection, since the thickness of the side steel armor of even the main battle tanks does not exceed 50-70 mm. So the installation of sandbags or construction debris on the thin side armor of armored personnel carriers and BMPs can provide sufficiently reliable protection against RPGs penetrating 250-300 mm of steel armor, however, only in the course [or may be heading] angles of 25-30°. Nevertheless, from the professional standpoint, such protection is difficult to call effective, since this level is reached by using an extremely large additional mass - about 3-5 tons if installing additional protection along the entire perimeter.
Another fairly popular and simple solution is the use of various “screens” [in english it should be called ”spaced armor”, I guess, but I will continue to call it in russian way] in the form of steel sheets, conveyor belts, etc. They have the same purpose - increasing bulletproof and anti-cumulative resistance. But usually these screens are made of conventional (non-armored) steel. Because of this, the increase of bulletproof protection will be appropriate. Thus, a simple/conventional bullet of a Kalashnikov rifle with caliber of 7.62 mm (ПС-43 bullet) easily breaks a sheet of construction steel with 10mm thick and does not penetrate an armor steel sheet with a thickness of only 4-4.5 mm.
The main purpose of such "screens" and especially screens from the conveyor belt and construction debris is to increase anti-cumulative protection. At the same time, their role is primarily to force grenades to explode at non-optimal focal length (the distance from the edge of the cumulative funnel [or may be in military terms it should be called “cumulative cavity”, I am not sure] to the obstacle).
However, the dependence of armor-piercing capabilities from the focus ("screen curves") for near to all RPGs, even of the old generation, is closed for public access, and the data given in the open literature varies a lot. The most reliable are the dependencies given in the second volume of the monograph "Physics of the Explosion" edited by. L.P. Orlenko (see the figure below).
Screen curves for cumulative munitions manufactured using conventional technology (1), precision munitions (2) and ideal munition (3 and 4):
L – depth/value of the armor-piercing,
F - the focal length,
D – the caliber of grenade.
It has long been known that armor-piercing capabilities of cumulative munition depend very strongly from the accuracy of manufacturing the warhead itself - a cumulative funnel, an explosive composition, an initiation point [of explosion], etc., since these parameters affect the formation of a cumulative jet. The slightest asymmetry in the design of the warheads leads to the deviation of any fragments of the formed jet from the axis, which is the reason for the decrease in its armor-piercing characteristics. The slightest asymmetry in the design of the warheads leads to the deviation of any fragments of the formed cumulative jet from the axis, which is the reason for the decrease in its armor-piercing capabilities. The effect of defects in the warhead is greatly enhanced when the grenade explode at some distance from the armor. Conventional cumulative grenades of caliber 65-73 mm at a distance of 600-700 mm from the armor lose their armor-piercing characteristics by 2-2.5 times, while precision grenades at such distances lose only small amount of their armor-piercing capabilities. "Ideal" munition, for which graphs are also given, are purely theoretical munition that does not have any defects. Their armor-piercing capabilities are determined only by calculation, and they in fact do not depend on the focal length to the armor.
The dependence of armor-piercing capabilities of cumulative munitions from the accuracy of their manufacture also leads to the fact that these characteristics can not be predicted accurately - they can only be calculated using statistical methods. Therefore, in the graph, the screen curves for conventional and even precision munitions have rather wide variance fields, which should be taken into account by the protection developers.
Tanks T-72B of Donetsk People Republic forces with "screens" from the conveyor belt on the front and stern (frontinfo.info).
BMP-2 of the Syrian government forces with additional "screens" made from concrete slabs.
The principle scheme of work of slat armor / "screens"
A fairly strong dependence of the armor-piercing capabilities of cumulative munitions from the trigger point leads to the fact that the installation of even conveyor belts (for example, on the forehead or stern of the tank) significantly increases the protection of the editorial and lower part of the stern of the hull. But further the influence of the focus decreases and even when the grenade explodes in 2-3 meters from the armor, its armor-piercing capabilities still remain at the level of 1-2 calibers, i.е. not less than 70-100 mm, which is dangerous for thin-armored structures.
Even more effective can be considered the use of not just the "screens" described above, but the so-called "powered", which not only explode the grenade at some distance from the armor, but also provide a certain reduction in armor-piercing capabilities. An example is the use of such screens on the BMP-2 of the Syrian government forces. Here concrete slabs of 100-150 mm thickness are used as a screens. With an dimensional coefficient of concrete Kr = 3.5, this screen is equivalent to 30-42 mm of steel for a cumulative jet.
Examples of additional protection for T-72 tanks taking part in military operations in Syria.
Special place in anti-cumulative protection is occupied by slat armor screens. Their design is very diverse, but they all work on the same principle - the destruction of the warhead of the grenade before it triggers. At the same time, either the fuse's electrical circuit is broken and the grenade acts as a simple blank or the grating deforms the lining of the cumulative funnel, and when a grenade triggers, a defective cumulative jet with significantly smaller breakdown characteristics is formed.
ПГ-7 grenade hits the latticed on-board screen of BMP-2. In both experiments, the grenades did not exploded. On the left photo you can see that the grenade, deforming the lattice, hit the armor screen installed behind the armor screen, without having any effect on the main armor of BMP-2. In the second experiment (photo on the right), an incapacitated grenade destroyed the latticed and armored screens. But the main armor BMP-2 is not punched. Only the trail from the impact is visible.
Hit of the ПГ-7 grenade into the latticed screen of the rear door of BMP-2. The grenade hit the edge of the lattice, grenade worked normally and broke through the armor of BMP-2. A small hole of the cumulative jet is visible on the door.
Variants of installing the "netting" protection SidePRO-LASSO of the RUAG (Switzerland) firm.
There is an opinion that the latticed screens should be made of high-strength armor steel in order to effectively destroy the body of the grenade. However, recent studies (conducted by both foreign developers and our domestic Scientific Research Institute of Steel) have shown that the strength characteristics of latticed are not so critical. Against grenades such as ПГ-18 and ПГ-7, "netting" screens are made of strong steel wire or aramid ropes. To destroy the thin-walled aluminum body of grenades their strength capabilities are quite enough. Much more the effectiveness of lattice and "netting" screens depends of the size of the cell or the distance between the lattice bars and the angle of interaction with the screen, which is well illustrated by the graphs given here.
Abroad, there have been a lot of developments of various lightweight versions of "netting" armor, whose effectiveness in cumulative grenades is even higher than traditional latticed screens. If the efficiency of latticed screens does not exceed 50-60%, the "netting" screens designs provide an efficiency of up to 60-65%. This is due to the fact that the probability of normal explode of the grenade on the "netting" armor is less than on a sufficiently thick lattice armor.
If the nodes of the nets are reinforced with metal washers, then the effectiveness of such a barrier is further increased, since the destruction of the grenade warhead is more intense. This effect was used in the Scientific Research Institute of Steel during the developing of the universal protective kit "Mantia". Its basis is the mass production masking radio-absorbing material "Nakidka" [“Cape”], on the back side of which with a certain interval fixed metal washers. In this case, the product begins to work and as an anti-cumulative screen. The grenade pierces the fabric structure of the camouflage cover without triggering and deforms on metal nodes. Such a universal kit is offered, for example, to protect trucks from their detection and from cumulative grenades.
The use of the Q-Net-II "netting" protection of Qinetiq North America firm.
Upgraded BMP-2M. As additional protection, latticed screens are used. Forum "Army-2015". (Photos by V. Izyurov and M. Pavlov)
Also we want to note that this variant [of protection] is much easier than the kit "Nakidka" with latticed screens, installed on one of the variant for upgrading the T-72 tank - "Rogatka".
Tank T-72 "Rogatka" with "Nakidka" kit and latticed screens (photo A. Khlopotov).
One of the variants of latticed screen - are various chain systems [also known as “chain-skirts”]. They are used where it is impossible to apply latticed structures. Such structures are used, for example, by the Israelis to protect the joint of the turret with the hull on the "Merkava" tanks, as well as the Poles on the modernization of the T-72 tank - RT-16. The same principle was adopted by the Syrian troops, reinforcing the anti-cumulative protection of their tanks. An interesting variant of the combined use of chains and latticed screens is used to protect the joint of the hull and the turret on one of the latest versions of the T-90 tank, known as the "Proriv-3" ["Breakthrough-3"].
Tank Т-90М «Proriv-3».
Fragment of the "Mantle" kit. View from the back.
The remains of ПГ-7 after overcoming the “Mantia” kit.
Installation of "Mantia" kit on the armored car.
T-72M1 of Syrian Republican Guard with additional protection in the form of latticed screens and chain-skirts.
In the Polish project for upgrading the T-72 tank - RT-16 – chain-skirts system are also include as additional protection.
The protection of the niche of the turret of the Israeli tank “Merkava-4” includes chains.
The situation is more complicated with the use of reactive protection [RA - reactive (dinamic in russian) armor]. Practically all "improvised" modernization variants with the installation of RA mean the use of 4C20 serial elements and different containers, which are installed in various ways on the protected projections [of armor]. Note that ERA [element of reactive armor] 4C20 was originally developed for tanks, and it was intended to be used on relatively thick armor capable of withstanding the powerful explosive effect of a joint blast of a grenade and several ERA 4C20.
Even in the late 1990s were made the attempts to establish this "tank" RA on the lightly armored vehicles, but all of them ended in a negative result. It turned out that without the use of additional measures to mitigate the explosive effect, the use of RA only increases the catastrophic damage from hitting of the grenade.
But in 2000 the Scientific Research Institute of Steel were able to create a workable RA complex for BMP-3 on the basis of ERA 4C20, using effective damping. But, firstly, the BMP-3 has a enough thick-armored hull made of an aluminum armor alloy, which is much more receptive to explosive loads than thin steel of many light armored vehicles [LAV], and secondly, the survivability of the complex itself was extremely low: hit of grenade broke several blocks at once, revealing large areas of protected projections. Unfortunately, this experience is still largely ignored by many amateur developers, which, as a rule, leads to a predictable result.
One of the first R&D "Contact-3" to install dynamic protection with ERA 4C20 on BMP-2, conducted by the Research Institute of Steel. Left - a break in the main armor when a PG-9V grenade hits the RA.
Nothing teaches as quickly as one's own sad experience. The latest developments of the Donetsk People’s Republic militiamen simply arouse respect, since they really improve the survival of the military hardware, which they are modernizing.
The Ukrainian Armed Forces are also making appropriate conclusions, so there are fewer blatant "blunders" today. Because of this, the modernization of the BMP-1UM offered by the Zhitomir Armored Factory is perplexing. If the crew of this vehicles had a chances to survive the hitting of a grenade, after the RA installation these chances are reduced to zero.
Ukrainian BMP-1UM with RA blocks on the sides of the hull.
Examples of additional protection for BMP-1 and ZSU-23-4 "Shilka" using in the Syrian conflict.
BTR of the Ukrainian army with RA blocks on the latticed screens and the result of hitting of the RPG grenade.
The problem of increasing the protection of the LAV, of course, was and remains a priority for developers of all countries. However, there are fewer and fewer available passive ways to increase protection. Against massively used screen screens, a simple solution has already been found: in conventional grenade, between the hull and the electrical conductor from the head piezo-detonator to the detonator an insulating spacer is installed, so that even if the head part is damaged, the fuse chain is not broken and the grenade works normally.
BMP-2 modernized by the Donetsk People's Republic militiamen. But it is unlikely that such a modernization will save the crew from the death of an RPG hitting.
In the Scientific Research Institute of Steel a great perspective in the use of dynamic defense capabilities are still seen. The developments of recent years have significantly increased the safety of reactive protection and minimized the negative impact of the explosion on the protected vehicles. This is achieved by using another explosive compounds and reducing their mass. It is enough to compare, for example, the characteristics of the first-generation ERA (4C20) and the next generation (4C24), which was developed in the early 2000s: the amount of explosives in it less is 2 times.
The comparison of characteristics of ERA 4C20 and 4C24
Additional protection of the joint of the turret of the T-72B and its hull in the Donbass by the installation of the ERA "Contact" on flexible screens. Evaluated by experts as a very successful and efficient solution (ursa-tm.ru).
Abroad, this type of protection has been and remains one of the priority for enhancing the protection of the LAV. Reactive protection for several generations has been applied to the “Bradley” BMP, the “Stryker” BTR, is part of the new German BMP “Puma”, is on the Spanish LAV, on the British BMP “Warrior”, and this list can be continued.
Russia, the first in the world to prove the possibility of using RA on LAV and has created such a workable complex for BMP-3, still does not have any RAK [reactive armor kit] for lightly armored vehicles, although the BMP-3 for protection requirements has long time ago lagged behind modern requirements. For the sake of preserving such characteristics as firepower and maneuverability/mobility, the developers, unfortunately, are not in a hurry to improve the protection of this machine. Meanwhile, BMP-3 armor is unlikely to protect even from modern 25 mm caliber guns.
Armor-piercing capabilities of modern small caliber cannons (autocannons).
40СТ – APFSDS of CTA telescopic round;
40SS – APFSDS rounds for 40mm cannons;
30 mm и 25 mm – conventional APFSDS – for cannons with caliber 30mm и 25mm.
An example of installing a neat screen with an ERA protecting the turret zone, where the placement of reactive protection is simply difficult, on the T-72B tank of militiamen of self-proclaimed Donetsk People's Republic (frontinfo.info).
But today, it seems, the situation starts to change - the issues of protection of lightly armored vehicles in Russia are beginning to be given due attention. So in some products on the "Kurganets" platform, for example, even reactive protection is prescribed.
Test of the dynamic protection kit with ERA 4S24 on BMP-3 at the Scientific Research Institute of Steel. Only one block of RA went out of action. 2004.
Armored recovery vehicle on the "Kurganets" platform with RA blocks.
Of course, in addition to reactive methods of protection, so-called "active" methods of protection are rapidly developing. Active protection systems detect and destroy the munition before it hits the armor, which is, of course, most preferable, so many developers of new military equipment are betting precisely on this method. However, we should not forget that in real combat conditions the simplest and most affordable means are sometimes the most effective, therefore sandbags, latticed screens and RAKs of the first generations were used and will be used. But it is important that these improvised funds are used competently and most effectively.
P.S.: As usual sorry for mistakes and thanks for attention :)