A common question on my video about the
effectiveness of Molotov Cocktails against tanks was the question if Molotov Cocktails could
set off the explosive reactive armor on tanks. Additionally, the question is, why there are
burnt out tanks that have explosive reactive armor blocks that were not set off and similarly why
this is the case with blown off turrets as well. First off, explosive reactive armor are these
little boxes and sometimes other shapes on Tanks. What do they do? They are intended to
defeat hollow or shaped charge warheads like the Panzerfaust, but also more modern anti-tank
guided missiles. There are also anti-tank gun rounds that use this principle, they are generally
called HEAT shells for high explosive anti-tank. A hollow charge explodes in such a way that
the directed explosion with the liner creates a jet that penetrates armor. The details are
important here, I once got this wrong myself: “Remarkably, contrary to popular myth, the
material that forms the jet is not molten but rather a stretching plastically deforming rod. It
is usually referred to as a ‘jet’ mainly because it is assumed that it behaves like a fluid in
the models used to simulate its behaviour.” Explosive Reactive Armor in a way follows
the principle of fight fire with fire: “Much in the same way that the formation of
a shaped charge jet is simple and elegant, its defeat by ERA is also simple and elegant.
Discovered by Manfred Held back in the early 1970s (Held 1970), the simplest construction of
ERA consists of two steel plates sandwiching a layer of high explosive (see Figure 9.2).”
Here you can see a simple example on how this steel high explosive sandwich is setup.
A while ago I saw photos of burnt out Russian tanks and I was baffled at first that although
the track wheels and other stuff was deformed and looked like it had melted or better
bent due to heat from the fire combined with the weight of the tank. Meanwhile,
the explosive sandwiches seemed all fine. I also had at one point briefly read that some
Russian tanks had their explosives missing from the explosive reactive armor, but I was
cautious, so I dropped TacError a line and he noted, that reactive armor generally is
designed so that it is not easily set off. Which makes a lot of sense, since if you
have a lot of them next to each other, one shot could create a chain effect or set
the explosive dominoes rolling and the whole protective setup would be rather ineffective.
So, I thought I would dig a bit deeper. Since it is called explosive reactive
armor, let us start with the explosives: “The choice of the explosive which is sandwiched
between the two metal plates is obviously most important as it must detonate when struck by
a shaped charge jet but not when an ERA pack is struck by bullets or shell fragments.
It should also not detonate due to a fire or field repairs involving welding. Detonation
must also be confined to the module struck by a jet and not allowed to spread by sympathetic
initiation to adjoining modules. Otherwise a single shaped charge hit would strip a tank of all
its ERA, instead of depleting only one module.” In that regard little has changed, the
Professor of Impact Dynamics Paul Hazell notes in his book about armor the following,
which includes a bit more information: “Modern ERA packages also must provide sufficient
protection against small-arms ammunition, and the explosive employed must be
sufficiently insensitive so that it is not detonated by fragments. Protection against
heat sources such as that provided by exposure to napalm is also desirable.”
He further adds the following: “Many countries, such as the United Kingdom, are only prepared to adopt insensitive
munition-compliant products in service. Explosives that are very difficult to accidentally
initiate are almost universally cast polymer bonded explosive (PBX)-based materials. These
materials are very difficult, if not impossible, to initiate unless a very violent stimulant
such as a shaped charge jet penetrates them.” Although be aware that Napalm probably could
degrade certain types of reactive armor. Keep in mind, it should not explode but
potentially the heat from napalm might be enough to burn them and/or expand them enough that
the metal containers eventually would break open. Tankolad notes about Soviet Kontakt-1:
“This essentially means that large areas of the tank may become unprotected
after it is doused in burning napalm.” Of course, now the question is, if explosive
reactive armor is almost as insensitive as a brick – which it often at least resembles from the
shape – how does it set off, when it should do so? Some fancy computers? Sensors? Well, actually
due to the nature of fighting fire with fire, this problem apparently solves
itself according to Hazell: “Due to the very high pressure region incurred
in the explosive composition by the jet, it is relatively simple to guarantee
initiation when desired whilst at the same time remaining safe at all other times.”
So, if explosive reactive armor works as generally designed a fire from a Molotov
Cocktail should not be able to set if off. Similarly, the tank slowly burning out neither.
This is also stated by Tankolad about the first generation Soviet Kontakt-1
explosive reactive armor: “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.” Yet, this brings us to the next question,
why is Kontakt-1 and others not set off, when a tank violently explodes? Well, I assume
this comes down to the simple fact that during such an explosion the reactive armor sandwiches
are on the opposite side of the explosion, which is behind the main armor of the tank.
So, they are rather well protected. Due to this all the pressure is released somewhere else.
Namely all the energy from the explosion goes out by the hatches or if the turret pops by the
turret ring. Since explosions go the way of the least resistance and the reactive blocks
sit on the other side of the most resistance. Yet, there is a minor problem now, since some
of you might know, that some explosive reactive armor, like the originally Soviet,
now used in Russia Kontakt-5 armor. Kontakt-5 also protects against armor-piercing fin
stabilized discarding sabot projectiles as well. As such, it is also called
universal reactive armor: “This is called universal reactive armor (UDZ)
since it degrades the performance of both APFSDS and HEAT warheads in contrast with the
first generation of Kontakt reactive armor, which degraded only HEAT warheads. This required
the use of a steel plate 4 to 10 times heavier than used in the first-generation Kontakt in
order to interfere with the APFSDS projectile.” This of course required a setup that the
armor-piercing fin stabilized discarding sabot, which is basically a large metal arrow, still
sets off the explosive module. Zaloga notes that this was achieved the following way:
“Kontakt-5 relied on a much more substantial steel plate on the outside of the panel and
this material was sufficient both to increase the degradation of shaped-charge jets, and also
degrade APFSDS penetration by about 20–35 percent. This plate required a more energetic explosive
insert, with a TNT equivalent of 0.28kg in the 4S20 panels of Kontakt-1 versus 0.33kg in the 4S22
panels of the Kontakt-5. The Kontakt-5 panels had to be properly angled for maximum effect and
in combination with their size and weight, they could not be bolted on, as had been the case
with Kontakt-1. Kontakt-5 had to be incorporated as a comprehensively designed armor package
that would have to be undertaken during original manufacture or during capital rebuilding.”
Similarly, Hazell notes: “Mostly, APFSDS-defeating ERA consists of heavier
and harder plates and larger volumes of high explosives. Probably the most famous example
is Kontakt 5 that has been deployed on T80Us and T90s. Some reports suggest that it adds 300
mm of equivalent RHA [rolled homogenous (steel) armor] protection against APFSDS rounds by the
propulsion of a 15-mm-thick front flyer plate. However, thicker plates mean that you
have to use thicker explosive layers.” Be aware that according to the German
Tank engineer Rolf Hilmes and other there are currently 4 different generations
of Soviet or now Russian explosives armors: First Generation is Kontakt-1, Second
Generation is Kontakt-5, third generation is Relikt and 4th Generation is Malachit.
And it seems that at least for Kontak-1 armor, the chances of chain reactions and/or setting
off multiple armor blocks at once is possible: “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
As mentioned, Kontakt-5 uses a more sensitive high-explosive, but it is protected by stronger
steel plates. As such, I suspect that Kontakt-5 might be less prone to such chain reactions,
but I could be wrong here. It seems that both Kontakt-1 and Kontakt-5 armor is used on
Russian tanks currently in the War in Ukraine. Although, finally it should be added, it
could also be that the explosive elements might be missing as well, but generally
a burnt-out tank that visually seems to have intact explosive reactive armor bricks
is not an indicator for missing explosives. To summarize, generally explosive reactive
armor is designed in such a way that it can’t be easily set off. After all, you don’t want
a machine gun burst or hand grenade that can strip your tank of its defense. This is achieved
by the use of rather insensitive high-explosives that are at the same time set off
by force of a hollow-charge jet. This generally also helps against chain-reactions
as well, if a block is set off as intended. Although we generally assume that fire sets
off explosives, this is clearly not the case with some explosives, e.g., C-4 plastic
explosives can’t be set off by burning. I hope you learned something new.
Thank you to Andrew for reviewing the script. Thank you to Tankolad for clarifying
information on napalm versus Kontakt-1. Special thanks to all my supporters for making trips to
museums and the military archives possible. As always sources are listed in the description,
thank you for watching and see you next time.
