Ukrainian „Nozh” Explosive Reactive Armor. Part I - Classic ERA types and methods of defeating them as a point of reference to the Nozh’s analys


Written by :,5,23,8445,wojska-ladowe,wypo

Translated by : Bzdziuchanson (me)

Part 2 is coming out next week (probably)


There aren’t many types of armor that cause such emotions in the broadly defined “tank community” as the Ukrainian solution known as “Nozh” (Knife) ERA and its further development known as “Duplet”. There are various aspects that cause such a situation. The most basic one is a very aggressive and visible advertisement campaign carried out by one of the main producers of the Ukrainian ERA – the MICROTEC company, which tries to get foreign buyers for its product due to insufficient amount of orders by the Ukrainian MoD. One way of achieving this is publishing advertisements that underline the advantages of home-grown ERA compared to for example Russian solutions.

On the other hand there was recently a strong marketing war fought between the Russian producer of T-72 family of tanks and its derivatives - Uralvagonzavod (Ural Wagon Factory) and its Ukrainian counterpart - Kharkiv Factory of Transportation Machine-building of Malychev - the producer of T-64 and T-80 tank families and their derivatives. Both factories compete in the enormous modernization market for post-soviet machines and for new orders from developing countries. The direct results of this competition are series of articles and counter-articles in the Russian and Ukrainian military press which are mostly based on the conflict between the Ural and Kharkiv factories which lasts since the times of the Soviet Union. There are also materials posted on two blogs – Ukrainian written by Andrei Tarasenko and Russian, written by Aleksey Chlopotov. Both bloggers are connected with arms manufacturers and fight for the interests of their national research and production centers.

Due to mentioned factors the amount of material about Nozh is wide but selective, since it often omits flaws of the Ukrainian ERA. On the other hand Russian publications, which often do not even try to debunk thesis presented, exaggerate some problems or even create non-existing ones. This causes informational chaos which makes it harder to write and analyze known facts honestly. We shall also remember that some parts are classified so any attempt of answering question about “Nozh” requires us seek analogies in currently known constructions and carries a lot of possible mistakes which the reader should be aware of.

“Classic” ERA from the USSR and Russia

It’s good to start describing “Nozh” with a point of reference first – for example heavy reactive armor types designed in the USSR/Russia, 4S22 (Kontakt-5) and 4S23 (Relikt). The overall working principle of every classic ERA is similar – it’s based on movement of metal elements of the ERA cassette caused by an explosion of reactive elements , this inflicts side stress disrupting the cumulative jet from a HEAT round or bending (optimally breaking) of an incoming KE penetrator. This overall principle is realized by different cassette’s structure. First, let’s look how Kontakt-5 ERA provides protection for Object 188 (T-90S tank).

4S22 Kontakt-5 scheme. Dark blue – external hardened metal
plate, violet – elements preventing the explosive inserts from moving, light
green – explosive inserts, light blue – cassette’s back plate and mounting
points. The explosive inserts are shown below the scheme. All pictures belong
to the author if not stated otherwise.

An incoming penetrator hits the external hardened plate and stabilizes itself when penetrating it. The fragments, pressure and the penetrator itself detonate the internal explosive elements when they reach them. The still moving penetrator reaches the back plate and also penetrates it – but in the same time the explosion causes the external metal plate to move “away” from the basic armor. It causes side stress in the penetrator making it bend (or in the best case break). It also causes the trajectory of the penetrator to change which makes it hit the main armor under angle. It makes the risk of the penetrator breaking larger and – by making the penetrating channel non-linear – decreases the depth of main armor that the penetrator can perforate. According to Russian sources the Kontakt-5 (introduced in 1987) is capable of reducing the penetration of APFSDS rounds by 20% and single HEAT warheads by 50-80%.

Weight of the complete ERA set on T-90S is 1,5 tons. The coverage of the frontal armor (for 0-35 degree angles) on T-90S and T-72B model 1989 isn’t great and oscillates around 44-55%. In other words an incoming projectile has a 50% chance of hitting a place not protected by ERA.

In case of a decade younger 4S23 Relikt the internal build of the ERA cassette is more complicated and the working principle is slightly more sophisticated. Hitting the Relikt’s cassette an incoming penetrator penetrates the external metal plate and detonates the internal explosive elements when it hits them. Due to the explosion the external armor plate starts moving “from” the basic armor like in Kontakt-5 but the novelty is a presence of another hardened metal plate located inside the cassette that starts moving “towards” the basic armor but then it gets amortized when it reaches second layer of explosives that initiate and make the plate move “from” the basic armor again.

So the Relikt’s cassette looks like this: external hardened metal plate – hollow space – 1st layer of explosives – hardened metal plate – 2nd layer of explosives – hollow space – back plate. The internal metal plate moves “towards” the basic armor, then it gets amortized on the second layer of explosives and detonates them thus making it move again “from” the basic armor. This creates a time interval between the movement of the external and internal metal plates. In theory it should allow (despite the ERA being initiated by HEAT warhead precursor) the internal plate to “catch” the main cumulative jet. In case of KE penetrators it causes double side stress to the penetrator which should optimally break both the top and back of the rod.

According to Russian sources the Relikt ERA should be capable of decreasing penetrating abilities of an APFSDS round by 40-50%, single HEAT warheads by 70-90%, around 50% for tandem HEAT warheads found in ATGMs and tandem HEAT warheads of RPGs by 95%. The weight of the entire Relikt ERA set on T-72BM Rogatka is ~2,3 tons. The frontal coverage oscillates around 55-60% for 0-35 degree angles.

Supremacy of Soviet armor?

The introduction of heavy Kontakt-5 ERA in 1987 caused a gap between the capabilities of NATO’s rounds and the armor of Soviet tanks. From theoretical point of view APFSDS and tandem HEAT warheads capable of penetrating heavy ERA were introduced in 1992-1994 thus creating an almost 6 year disproportion between the Soviet “shield” and the NATO’s “sword”. Another fact worth noting is that the basic armor of Soviet tanks was already largely immune to APFSDS rounds, majority of RPG’s and some ATGM’s warheads. A good example is the basic armor of the hull and turret of the export version of Object 478B (T-80UD from 1991) including both steel and ceramic elements it is over 620 mm RHA vs APFSDS and over700 mm RHA vs HEAT. By adding Kontakt-5 ERA the protection level is further increased – especially against HEAT warheads. Similar high protection is for T-72B model 1989 when the sum of only passive hull armor elements gives over 600 mm RHA vs APFSDS.

Presented situation was theoretically very dangerous for western AT rounds but it was lowered by few factors – rather large weak zones in the frontal armor and not thick enough coverage by ERA cassettes. In reality every tank has various weak zones which can be penetrated by older ammo. In case of T-72 family these are: gun mantled, gun mounting area, coaxial MG, turret roof, commander’s observation copula, turret ring and the lower hull glacis.

These weak zones are shown in a résumé of an article printed in the internal bulletin
of the Armored Forces of the USSR. The article states about advantages of tanks
with welded turrets in terms of better crew survivability. What’s important is
that T-72B (Object 184) was used as a reference point and its weak zones were

T-72B weak zones

The areas marked in red were considered weak zones and could be
penetrated by 3BM26 APFSDS which was introduced in 1984 and penetrates 380-410
mm RHA at 2000 m for 90 degree sloped target. The marked areas were penetrated
by this projectile from:

- driver’s hatch – 1700 m,
- turret roof – 3700 m,
- commander’s copula – 3900 m,
- gun mantled, gun mounting area and coaxial MG – 1650 m

In the article there is a statement that for 1000-2000 m range the probability of penetrating the T-72B frontal armor by an APFSDS penetrating 250 mm at 60 degree (a bit more than 500 mm for 90 degree) shot from Leopard 2 L-44 gun is over 45%. The stated penetration suits the German DM-33A1 APFSDS hitting the target at 800-1000 m range (typical for engagements in the Fulda Gap). Of course during combat a tank rarely moves straight. That’s why even slightest turret or hull move would cover the weak zones from the article. However, the example from the bulletin shows that measuring tank’s armor in RHA does not tell us everything about its protection level because even older ammunition can still be lethal.

The fact that Soviet tanks received their ERA kits also didn’t eliminate the weak zones, additionally the front coverage (except for T-80U and T-80UD) by heavy ERA has a lot of gaps and covers only around 45-55% of the front for -/+ 35 degree angles for the tank’s longitudinal axis.

T-72B3 tank. Green – area protected by the Kontakt-5 ERA, red – “weak
zones” from the Bulletin of the Armored Forces from 1991. Except for a small
portion of the roof the areas do not cover each other almost at all. Photo : Vitajin Kuzmin.

Due to these problems with Soviet tank protection we shall not write about the supremacy of Soviet armor over the penetrator, although the theoretical effectiveness of both APFSDS and HEAT rounds was not enough to defeat tanks introduced in the Soviet Union after 1987.


Solutions to defeating ERAs were mass introduced in the yearly 90’s. In case of APFSDS rounds there are three basic ways of reducing the ERA efficiency. First one is giving the top of the rod a special “skewer-like” construction and hiding it under a ballistic cap.

Experimental, modified 3BM22 Szpilka APFSDS which was capable of penetrating Kontakt-5 ERA without initiating it.

The top of the rod looks like cylinder with a length of 50 mm and wchich cross section has a diameter of 13,8 mm. This way of defeating Explosive Reactive Armor uses the fact that Reactive Armor usually does not explode when hit by 20-30 mm rounds even if they perforate the cassette. The job of such a rod top design is to simulate a small caliber round and gradually increase the penetration channel without making the explosive elements inside the ERA explode. The following solution was designed in the Soviet Union and tested on modernized 3BM22 round which was penetrating the Kontakt-5 ERA without initiating it. In the serial production the round was supposed to have this “skewer-like” rod top under a ballistic cap or a light ballistic cap that would become the “skewer” during ERA penetration. Currently such a design is probably used in the British CHARM-3 120 mm APFSDS and KE-W 120 mm APFSDS by ATK. A similar design is visible on German patents from 1992 which describe a new type of APFSDS round capable of defeating heavy ERA and multi-layered armor. This technique may not be viable against ERA with an additional hardened metal plate inside – like 4S23 Relikt.

Another way is using rods in “jackets” – which have the core made out of Depleted Uranium or Tungsten sinter in a matrix of other metals – steel or Tungsten alloys with different mechanical properties.

Such rods have a low probability of breaking even if facing serious side stress from
exploding ERA elements. Of course the rod will be bent and will fly a different trajectory after such a meeting which will surely reduce its penetrating abilities by some percent but it’s still better than breaking. It’s probably the most widely use method of reducing the effectiveness of Reactive Armor. On the other hand it has its limitations and its effectiveness against modern ERA with two or more non-linear moving steel plates (like in Relikt) is rather disputable.

A mono-block penetrator (on the top) and penetrators with “jackets”
(below) after passing a simple Non Energetic Reactive Armor (NERA) made out of
3 mm steel + 3 mm rubber + 3 mm steel layers.

The third way of defeating Reactive Armor is making the rod of an APFSDS round from multiple segments. When such a rod hit ERA the first segment “breaks off” and before the explosive elements initiate it “punches” a hole in the ERA elements equal to its length. The size of this hole is big enough for the rest of the rod to “fly” through it without being affected by ERA explosion. Such a way of defeating ERA was described in the US patent number 6,662,726 from 16 December 2003. There is also an EP 2 597 416 A2 patent showing a concept of a penetrator (very similar to M829A3) equipped with a “heavy” ballistic cap capable of acting as the penetrating segment described in the first patent. Use of such a design has one significant disadvantage – the segment that “break off” and punches a hole in ERA elements does not take part in penetrating the tank’s basic armor thus the rounds penetrating capabilities are lower the bigger this segment is. On the other hand losing 15-20% of the rod’s length for defeating ERA can be acceptable when we consider how much the explosion of ERA would affect the rod.

The way of defeating ERA shown in US patent number 6,662,726 B

Probably modern APFSDS rounds use more than one way of penetrating ERA. For example German DE 43 23 482 A1 patent of an APFSDS round from 1992 shows not only a special rod top and ballistic cap, capable of penetrating ERA without initiating it, but also the rod made out of multiple segments.

HEAT warheads vs ERA

In case of HEAT warheads (used mostly in RPG’s and ATGMs) the main way of defeating ERA is using a precursor. Precursors are divided into initiating and non-initiating ones. The first ones are supposed to make the ERA explode before the cumulative jet from the main charge reaches the armor. The main disadvantage of this solution is a need to create a relatively large time interval between the explosion of the precursor and the main HEAT charge. It must be done in order to give time for ERA to blow up after being initiated by the precursor. In reality majority of modern ERA (Relikt, ERAWA-2, BLAZER, ARAT) have multiple layers of reactive elements between metal plates and the time each layer explodes is delayed thus initiating precursors are nowadays most likely outdated.

More effective are the non-initiating precursors used in PzF-3IT600, RPG-29, RPG-28 and Kornet ATGMs. Their job is to “punch” a hole in ERA layers without initiating them allowing the main HEAT charge to pass through. Publications presented below show results of tests of penetrating two ERA layers covered by 14 mm armor plate by a precursor without initiating any of them. This precursor type allows the main HEAT charge to blow up right after without any time delays and the use of different layers and heavy moving armor plates in ERA can bring little effect against it.

Tests showing an example of defeating ERA by a low density cumulative
jet. It makes a large diameter hole in reactive armor elements without
initiating the explosives.

Another way of defeating ERA by HEAT rounds is the optimization of cumulative charges and increase of their parameters. Typical HEAT charges from the late 80’s penetrate 6,5-7 times the size of their insert’s diameter by creating a cumulative jet going from 6500 to 8000 m/s. Modern optimized charges using Molybdenum or/and
new explosive elements like PBXW-11 or LX-14 can create a cumulative jet going from 10500 to 12000 m/s and penetrating over 10,5 times the diameter of their inserts. Additionally the majority of the “penetrating force” of a cumulative jet is in the first 30% of its length. This makes metal elements from 90’s ERA too slow to “catch” and disturb such a fast cumulative jet.

Additionally the increase of penetration level for HEAT warheads is over 30% since 1990 which makes ERA even less effective. Of course such fast, advanced cumulative jets are used only in the newest HEAT warheads that are currently introduced into service. In order to oppose these threats a new generation of ERA emerged.

Difference in old and modern jet speed and its ability to penetrate
classic ERA.

Due to facts presented above Kontakt-5 ERA is currently not very effective against both HEAT and APFSDS introduced in the seconds half of the 90’s. Additionally Kontakt-5 is not effective against HEAT warheads with a precursor. For example the manufacturer of the PzF-3IT600 claims in its advertisements that their weapon can penetrate the frontal armor of the T-80U with Kontakt-5 ERA. What’s interesting is that the armor cross sections show not the T-80U (Object 219) armor, but the one belonging to newer and better armored T-80UD (Object 478B). The protection level of both tanks (based on the factory draws) against HEAT rounds is 620 mm RHA (for T-80U) and ~730 mm RHA (T-80UD). These values are lower than the penetration level of PzF-3IT600 110 mm warhead (producer claims it penetrates over 900 mm of RHA). It seems that claims made by Dynamit Nobel are true and in case the precursor deactivates Kontakt-5 ERA the armor will be penetrated.

On the other hand Panzerfaust-3IT600 turned out to be too weak against Polish ERAWA-2 and lost almost half of its declared penetration after passing the ERA. Younger Kontakt-5 Russian ERA were also created with newer HEAT warheads with
precursors in mind so we shall not say that ERA will be “totally” ineffective against tandem HEAT warheads. Even the Ukrainians (big enemies of Russian Relikt) claim that Relikt ERA can reduce penetration of tandem HEAT warheads by 50% and if we take the low effectiveness of PzF-3IT600 against ERAWA-2 into account they might be true. We shall also remember that lowering penetration of a HEAT warhead by 40-50% might be enough to protect the vehicle from being penetrated since there is also the basic armor of the tank after ERA.

Panzerfaust-3IT600 and T-80UD armor cross sections that it penetrates.
By Dynamit Nobel

Kontakt-5 and Relikt ERA presented in this part are
just one branch in the entire tree of armor solutions being developed since the
times of USSR. There were R&D works performed on at least two types of ERA
– “classic” ERA with metal plates being moved by explosion and on ERA using
linear shape charges, where the cumulative jets were supposed to act like the
hardened metal plates from “classic” ERA.

It’s the second group inside of which we shall seek
the Nozh’s grandfather that will be described in the next part of the article.