Ukrainian "Nozh" Explosive Reactive Armor. Part II - "Nozh" and "Duplet"

Written by:,5,23,8552,wojska-ladowe,wypo
Translatation by: Bzdziuchanson - read it first

Part III coming out next week
The “Nozh”
Explosive Reactive Armor has been created due to co-operation of three
Ukrainian institutes – the “MICROTEC” company (more precisely National Center
of Critical Technologies “MICROTEC”), the second was the world-famous Paton
Electric Welding Institute (Research and Engineering Center of Explosive
Materials of the Paton Welding Institute of the National Academy of Science),
the last one was the Kharkiv Machine-building Factory of Malychev (more
precisely Kharkiv Machine Construction Bureau – ChKBM).

The creation of “Nozh”

We shall
seek the “Nozh” ancestors among solutions developed back in the times of the
USSR. There happen to be photos of projects from the 80’s that have a similar
working mechanism – linear cumulative charges bent in triangular shapes and
place inside an ERA cassette. This type of solution has also been presented by
the Russian Research and Development Institute (NII) Stali.

cassette. Photo: Microtec.

We can assume the effectiveness
of such ERA design thanks to a polemical article written by A. Tarasenko and
published as a response to Russian articles about “Nozh” . The publication
consists of two ERA schemes developed by NII Stali (during the time of the
USSR) which look very similar to ERA presented by NII Stali in Omsk in 1999.
The cumulative insert bent triangularly from these ERA has such a scheme : 2 mm
of copper + 6 mm of explosive material + 2 mm of copper. Space between them is
filled with material that was supposed to prevent any movement of elements. The
presented designs had one major difference – a 20 mm thick external metal
plate. The more effective ERA version was supposed to reduce penetration of an
unknown warhead by 40% but there is no info about how effective this ERA was
against APFSDS. Probably the engineers from NII Stali have decided that ERA
based on movement of metal plates caused by explosion is the future and ERA
based on triangularly bent cumulative inserts ended up us a trivia presented on
military expos and conferences.

The theoretically “worse” way
(linear charges instead of “classic” ERA based on movement of metal plates) has
been chosen by the Ukrainian engineers. It resulted in the creation of “Nozh”
almost two decades later and its further development known as “Duplet” which
eliminates the flaws of ERA designed back in the USSR.

Pictures of an
experimental ERA from the 80’s (above) and ERA presented by NII Stali in Omsk
in 1999 (below). Photos : and NII Stali.

To understand how “Nozh” works
we shall first know how linear cumulative charges operate. Linear charges are
mostly used by sappers or miners (to cut metal structure). When used for
engineering work they mostly come in a
form of ready to use coils of already formed explosive charges that can
be cut based on their purpose. The cumulative insert is made from copper or
aluminum and has an apex angle of 60-90
degree. There are also more advanced types of linear charges using a filler and
a double copper insert. The focal point of such a charge is usually equal to 3
times its caliber and its metal-cutting abilities are proportional to the size
of the charge.

In case of “Nozh” a largely
modified derivative of such charges is used. There are at least three types of
cumulative inserts used in “Nozh” cassettes. They have different size, insert
elements, reaction time and speed of the cumulative jet they form. The shape of
the cumulative charge is also different – it looks like a Moon crescent.

Examples of
linear shaped charges used to cut steel constructions. Johnston M., Lim S.,
“Numerical Observation of the Jet Flight Patterns of Linear Shaped Charges”.

The “Nozh” ERA looks like this.
Inside of a thin cassette there are linear charges placed next to each other,
underneath them there is a double ultrafast detonation path connecting them and
under the path there is a foam filler keeping everything in one place.
Depending on the material which the cumulative insert is made of and type of
explosive elements the top of the
cumulative jet created can reach speeds of 5400-12300 m/s.

The theoretical working
principle of “Nozh” looks like this: an incoming KE penetrator going 1500-1800
m/s or a cumulative jet from a HEAT charge going 6500-10000m/s penetrates the
cassette and hits one of the linear charges initiating it. Through the
ultrafast detonation path a detonation signal is transferred to all remaining
cumulative charges inside the cassette. The penetrator passes the initiated
charge but due to explosion of remaining charges it gets “chopped” into pieces
by cumulative jets and further damaged by explosion of the charges.

There are three different types
of cumulative charges in “Nozh” ERA. They do not only differ in size (aka
“cutting” power) but also in the type of material used inside the cumulative
insert or the explosives. This means different reaction times and speed of
created cumulative jets.

The first theory has two flaws.
First is the effectiveness of charges against APFSDS rounds. The penetrator
will initiate the charges already being inside one of them. The explosion of
remaining charges will surely have some little effect on the penetrator but we
shall forget about “chopping” it into pieces by the cumulative jets because
only three to two surrounding charges (depending on the hit angle) will create
jets hitting the penetrator in their optimal focal point. A little tip here can
be found in the Czech APS – EFA system which also uses linear cumulative
charges but they are ignited by special sensors. Thanks to this they can choose
the optimal (considering the focal point of the cumulative jet) moment for
charge explosion. The EFA active protection system can reduce the penetration
level of APFSDS rounds by 30-35%. Similar (if not lower) should be the
effectiveness of charges found inside the “Nozh” cassette. In case of HEAT
warheads the disruption of the cumulative jet is even easier and can be
achieved by the linear charges themselves but because the majority of the
penetrating “force” is in the first 30% of the cumulative jet’s length the
speed of “Nozh” cumulative jet formed from linear charges should be much higher
than 6000 m/s. It is possible only for inserts made out of Aluminum, Molybdenum
or Nickel – in case of such materials the top of a cumulative jet formed from
the linear charges would achieve speed of over 9000-10000 m/s.

How do these points correspond
to the effectiveness of “Nozh” ERA? The producer declares that his ERA can
reduce penetration of APFSDS rounds by 80%, single HEAT warheads by 80% and
tandem HEAT warheads by only 20%. The not so great effectiveness against tandem
HEAT charges is compatible to what we know about the build and working
mechanism of “Nozh”, the Czech EFA and linear shaped charges in general. Such
great reduction of penetration of APFSDS and non-tandem HEAT rounds can’t be
achieved only by linear shaped charges so we shall seek for other mechanism
that are used in Ukrainian ERA.

The secret
of Nozh ERA – relatively thick external metal plate of the cassette. Due to
explosion of linear shaped charges it forms multiple fragments that hit an
incoming rod or a cumulative jet. Photo: A. Tarasenko via Microtec.

It turns out that the secret is
a forced fragmentation of the external metal plate of the ERA cassette. On
pictures from tests and from ERA sets mounted on tanks we can see that the Nozh
insert (with linear shaped charges) is placed behind the frontal metal plate of
the cassette which is made of 15 mm of High Hardness Steel. At firsts it seems
that such a design reduces the effectiveness of shaped charges since at least
half of their “penetration” is lost to “cut” through the external metal plate
of the cassette. But it turns out that the shaped charges not only “cut” the
front of penetrator from its rest but are also used to explosively form a
series of fragments from the external metal plate. The explosion of ERA makes
these fragments hit an incoming penetrator “from blow” making it bend, break,
fall of the trajectory (in case of kinetic energy rounds) or disrupt a
cumulative jet (in case of HEAT warheads). The number of such fragments formed
from the external metal plate equals to the amount of cumulative shaped charges
minus one. The fragments have the length of the Nozh cassette, thickness equal
to the thickness of the external metal plate and width equal to the distance
between the centers of symmetry of two proximal linear shaped charges.

Scheme of
Nozh ERA during work. An optimal situation is shown when an incoming penetrator
hits the upper part of the cassette and
looses over 60% of its length.

According to information
presented above the working mechanism of Nozh ERA looks like this (in case of
an APFSDS round):

1. An incoming penetrator hits the ERA
cassette. Penetrates the external metal plate and hits the insert with linear
shaped charges initiating one of them.

2. Through an ultrafast detonation path
all linear shaped charges initiate, the penetrator moves forwards and pierces
the cassette.

3. One of the linear charges that’s
next to the one hit by the penetrator hits the penetrator being in its optimal
focal point and “cuts off” the top of the penetrator from its rest. At the same
time the remaining linear shaped charges “cut” the external metal plate of the
cassette into pieces. The explosion of shaped charges makes these fragments
move “away” from the cassette. Very fast cumulative jets move further forwards
and hit the penetrator but only the two-three jets from linear charges placed
next to the one hit by the penetrator are able to damage it – the rest of
charges can’t do so since they’re not in their focal points and their
penetrating abilities after passing the thick external metal plate are abysmal.

4. The top of the penetrator “cut off”
by a cumulative jet (5-7% of its length)
moves forwards and hits the main armor but the rest is hit from downside by the
fragments formed from the external metal plate. They are able to damage the
penetrator because it has already been hit by residual cumulative jets. The
fragments also change the trajectory of the penetrator.

5. As a result the main armor is
perforated only by the top of the penetrator (5-7% of its length) – the
remaining part is cut off, chopped into pieces (or highly damaged) by fragments
of the cassette. The explosion and fragments also change the trajectory of the
penetrator which hits the main armor not straight. This causes further damage in the penetrator
which should just break into pieces.

In other
words – the effectiveness of Nozh depends highly on fragments from the
“chopped” external metal plate. The linear shaped charges also reduce the
penetration of an incoming penetrator but the effect is smaller than the one
caused by fragments of the cassette.

As a result Nozh ERA is more
destructive for APFSDS rounds than any other ERA. Even Russian 4S23 Relict is
weaker than linear shaped charges and fragments of the external metal plate
hitting the penetrator from below like in case of Nozh.

On the other hand there is
little information about effects of Nozh elements on cumulative jets. Single
Nozh cassettes are surely weak against tandem HEAT warheads and modern HEAT

Another point is that the
effectiveness of Nozh depends highly on the place where the penetrator hits the
cassette. The scheme shown above represents a situation when the penetrator
hits the upper 1/3 of the cassette. As a result it gets hit with 5 fragments
formed by 6 linear charges. It causes damage in at least half of the
penetrator. Furthermore, Nozh cassettes on tank’s hull are very long and fit
two inserts thus the penetrator hitting the upper part of the cassette should
be damaged by fragments on its entire length. In theory it should cause a
destruction of the penetrator and the declared 80-90% reduction of APFSDS
penetration might be true. But in case the penetrator hits the lower 1/3 of the
cassette the effectiveness of Nozh is way lower, the scheme below represents
such a situation.

An example
of a situation when Nozh ERA has the lowest effectiveness – the penetrator hits
the lower 1/3 of the cassette. The penetration should be reduced by around 30%
in this case.

The situation presented on the
scheme above in theory should cause damage to “only” 1/5-1/4 on the penetrator.
In case of cassettes placed on hull such a situation has a 7,3% chance to
happen, in case of turret modules it’s higher and oscillates around 22%. The
penetrator hitting the lower part of the Nozh cassette (more precisely two
cumulative charges placed at the bottom) will suffer less damage (around 30%
less penetration - which is still a good value). This dependency on where the
penetrator hits the cassette is a natural consequence of the working mechanism
used in Nozh but this fact is omitted in Ukrainian articles. Probably these
flaws of ERA caused a decision among Ukrainian engineers to double the layers
of Nozh – in case of Oplot-M (Object 478 DU10) the layers on the hull are
doubled and the entire module looks like this – 15-20 mm metal plate – 1st
insert with cumulative charges – 2nd
metal plate – 2nd insert with cumulative charges – basic armor of the
tank. The side modules also have double ERA layers but the most interesting
modules are the ones placed on the turret which house four layers of inserts
with cumulative charges thus the penetrator will always be affected by two
layers of ERA independently on the place it hits the module. Thanks to this
even if the penetrator hits the lower 1/3 of the module it will still be
affected by two layers of ERA. The doubling of ERA layers will probably render
precursors and methods of defeating ERA (from the first part of the article) useless. The
“skewer-like” rod top will be destroyed on the first layer of ERA and will
activate the second layer and even segmented rods will be affected by
activation of two ERA layers. Similar are the chances of precursor found in
tandem HEAT warheads against Duplet ERA (basically doubled Nozh ERA with
different types of inserts in different layers). In case of Duplet the producer
claims that is reduces the penetration of both APFSDS rounds and tandem HEAT
warheads by 80% which might be true.

module from Oplot-M tank (Ob. 478 DU10) – we can see four layers of inserts
separated by a light filler. Photo: Morozov, drawing- Author.

Way lower is the protection of
modernized tanks from the T-64 family. In case of T-64B1 and B1M (these
vehicles were supposed to go to Africa) due to weight reasons both the turret
and hull have only one layer of Nozh ERA. The result is lower protection
against tandem HEAT warheads (~20%) and variable protection against non-tandem
HEAT warheads and APFSDS rounds (30-90%).

In case of the T-64BM Bulat
(Object 447AM-1) there is also only one layer of Nozh ERA on the hull and
turret. This makes the protection of these vehicles very non-explicit. On one
hand T-64BM Bulat and T-64B1 are quite well protected against APFSDS rounds
from the 90’s and non-tandem HEAT warheads but the protection is highly
dependent on where the penetrator hits the cassette. Long modules one the hull
provide better protection than short modules on the turret. In case of short
modules on the turret even newer ammunition unable to penetrate ERA can be
lethal depending on the place of impact. The designers of T-64BM Bulat were
apparently aware of this issue and placed an additional layer of 80 mm of High
Hardness Steel (~100 mm RHA) behind the turret Nozh modules. Additionally,
contrary to a false impression of good frontal coverage by ERA (in comparison
to T-72B3) the front of T-64 Bulat has plenty of weak zones not protected by
ERA. The overall protection is even lower since a single layer of Nozh are not
able to effectively protect against modern tandem HEAT warheads and probably
against segmented rods of APFSDS rounds. Therefore Ukrainian claims that T-64BM
Bulat has a protection equal to protection of current III+ gen. of MBTs seems
to be false.

The use of Nozh ERA on Oplot-M
and T-64BM will be described in the 3rd part of the article.

Nozh ERA – effectiveness

In case of a single Nozh layer
it seems that the effectiveness against non-tandem HEAT warheads and APFSDS
rounds is around 80%. Based on the working principle and analysis of Nozh this
value should be corrected to 30-80% against APFSDS depending on the impact place.
In case of HEAT warheads the value would also be a variable but the lower bond
remains unknown with the amount of information about Nozh we currently have.
The low (20%) effectiveness against tandem HEAT warheads seems to be
overestimated and can be true only for long modules placed on the hull. In case
of turret and side modules it can be lower than 10%. No effectiveness of
Russian Relict and Kontakt-5 ERA against artillery and aviation sub-ammunition
presented on the diagram below is a
marketing curiosity and should not be considered true.

In case of newer Ukrainian
Duplet ERA the doubled layers of cassettes with different types of linear
shaped charges with different diameters the speed of the cumulative jets and
the amount of fragments from the external metal plates are larger thus the 90%
protection provided by Duplet is probably true.

A diagram
presenting effectiveness of different ERA types against different threats:
non-tandem HEAT warheads, tandem HEAT warheads, APFSDS rounds, artillery and aviation
sub-ammunition. Drawing: A. Tarasenko via Microtec.

In case of Duplet ERA placed on
Oplot-M the protection provided by ERA is probably the highest of any known ERA
types but a single layer of Nozh is disappointing. Except for APFSDS rounds
(based on the place of impact) any other characteristic is not better than the
old Kontakt-5 ERA. Even the Polish ERAWA-2 provides way better protection
against tandem HEAT rounds, artillery and aviation sub-ammunition and
Explosively Formed Projectiles (EFP).

The price of Nozh efficiency
against APFSDS rounds is a non-acceptable mass to protection level ratio. The
weight of the entire ERA set on Russian T-72BM Rogatka weights 2300 kg, on the
highly covered by ERA Polish PT-91 it weights 2014 kg and in case of T-64BM
Bulat the ERA weight is 3500 kg(!).

T-64BM Bulat is fatter than
T-64BW by only 2,5 tons, but if we consider the difference in mass between
Kontakt-1 and Nozh ERA it turns out that the mass of reactive armor increased
by 3500 kg. This value is very high compared to protection offered by a single
Nozh layer. In case of Oplot-M the Duplet modules weight even more – around
5000 kg for the reactive armor alone but it seems that using modern composite
armor with smaller mass can provide similar protection for the hull and turret.

Summary protection provided by
Ukrainian ERA is not explicit. Ukrainian advertisements usually are dominated
by fascination of Nozh when in reality only protection against APFSDS is
good. The bad weight-protection ratio
and low effectiveness again tandem HEAT warheads as well as dependency on the
place of impact make us think why was this type of ERA rejected in the USSR at
the end of the Cold War and why was its development continued in Ukraine. The
single layer of Nozh ERA provides protection against APFSDS and HEAT warheads
between 30-90% (the value is for APFSDS) which is very good, the problem is
that non of the “big players” makes such weapons anymore. Modern ATGM like
Kornet, Metis-M, Javelin, Spike have tandem HEAT warheads with non-initiating
precursors. The same when it come to Nozh effectiveness against modern APFSDS
rounds that were designed to defeat ERA (DM63, M829A3, KEW-A3, M338, Sniwiec-1
and 2).

Against such threats Duplet ERA
has been designed – two different layers of ERA being a derivative of Nozh. In
this case the claimed effectiveness of 90% might be true – but the price is a
very high weight of the ERA set.

In the last (3rd) part of the
article the protection of T-64BM and Oplot-M tanks will be analyzed and first
conclusions from the use of Nozh in Donbas war will be drawn.