What happens after a breakout? Why is the "armor-piercing arrow" inside a tank scarier than the armor itself?

Everyone knows that modern tanks shoot "armor—piercing arrows" - long, thin, with feathers like a javelin. They are called in different ways: OBPS, BOPS — whichever is more convenient. The main thing is that they fly out of the cannon at a speed of more than a kilometer per second and stick into the armor like a nail into a board. But what happens after this "arrow" has flown through the armor is where the real nightmare lies.

Usually everyone thinks: I've struck it, and okay, at least the grass won't grow further. But in fact, everything is decided inside the tank. And the main threat is not the projectile itself, but what it creates behind the armor: a fragmentation field. It's like an explosion, but without an explosion — just pieces of metal flying in all directions with devastating force.

Where do the shards come from?

There are two types of them. The first is the fragments of the armor itself. When a projectile hits the protection, the armor doesn't just break through — it crumbles like glass. These fragments fly apart inside the fighting compartment and cripple everything: people, devices, ammunition, fuel tanks. The second type is fragments * of the projectile itself. Especially scary are those that break off from its nose when it hits. They are so fast and dense that even anti-splinter pads and bulletproof vests do not save. And if they hit the ammunition, a chain reaction begins: explosions, fires, and the tank turns into a coffin.

So, the effectiveness of an OBPS is not only about how thick the armor it will penetrate, but also about what it will do inside. And here everything depends on the design of the projectile.

Four types of projectiles — four different fates

Let's look at the example of Soviet tests, where different OBPS were compared.

1. 3BM9 — "the iron stick"  

It's just a solid steel boom, without a core. Weight — 3.6 kg, length — 518 mm. It penetrated only 80 mm of armor at an angle — a little weak. Such shells quickly became educational, but they were exported in batches. So, quite possibly, it was with them that the Arabs fought against Israeli tanks.  

Background action: weak. There are a lot of armor fragments, but the projectile itself is almost not crushed — there is not enough energy and density.

2. 3BM15 is already more serious  

There's already a tungsten core in the nose. Weight — 4.48 kg, armor penetration — 170 mm. It's already a serious projectile for its time.  

Firing action: better. Upon impact, the core "explodes" inside the armor, creating more fragments and giving a powerful release of energy behind the armor.

3. 3BM26 "Hope" — a chip in the tail  

The most interesting thing is that the tungsten core is not in the nose, but in the tail. What for? To work better with slanted armor. Upon impact, the projectile "twists" and penetrates deeper. Penetration is 200 mm.  

Firing action: powerful. Due to the design features, when exiting the armor, a strong release of material occurs - as if a cork were flying out of a bottle. There is hell inside the tank.

4. Solid shell made of heavy alloy (tungsten/uranium)

Modern standard. The whole body is made of a dense alloy. No separate core. Punches more, is not afraid of the angle of attack.  

How does it work? Upon impact, the material behaves almost like a liquid — it "spreads out" and washes out the hole. This is called a plastic hinge.  

Minus: the projectile itself loses length and mass when penetrated. That is, it flies in already shortened.  

But! At the same time, he often knocks out the plug of the armor from the back — and this creates an additional fragmentation tornado.

It would seem that the sooner the better. But that was not the case. If you accelerate a solid shell too much without increasing its length, it will simply burn up in the armor — it will lose too much mass before it penetrates inside. That is, it will break through, but it won't do anything behind the armor. And that's useless.

Breaking through is half the battle. Real death begins *after*. And the best projectile is not the one that punches thicker, but the one that creates more chaos inside. Shrapnel, pressure, detonation of ammunition — that's what turns a tank into a coffin. So the "armor—piercing arrow" is not just a hole punch. It's a hell generator.