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Know It All: HEAT Weapons -- How To Stop A Tank

Published in Geare magazine, Issue #48, 2008

The idea of a man on foot (and, yes, it normally is a person of the masculine persuasion) stopping a tank is, frankly, ludicrous.

Oh sure, as the Chinese 'Unknown Rebel' demonstrated back in 1989 in Tiananmen Square, a brief pause in their progress may be possible when the international media's cameras are pointing in the right direction. But what I'm actually talking about is a man, or perhaps two men, destroying a tank.

Back during the World War II -- the war in which the tank truly came into its own -- the main attack against tanks was carried by artillery, ranging from 50mm to 122mm designs. These used a combination of mass and velocity to penetrate the thick armour of tanks. This is no easy feat. The German Tiger tank of WW2 carried steel armour ranging from 25mm to 110mm thick.

The British responded with the '6-Pounder' artillery piece. For antitank use it flung a 57mm diameter solid projectile at nearly 900 metres per second. The amount of kinetic energy delivered to the point at which it struck the tank was roughly the same as some 350 British infantryman firing .303 rifles simultaneously at the same point.

More recently the former Soviet Union and the current United States have upped the mass of their antitank kinetic weapons by using depleted uranium, which is in abundance as waste anyway. Depleted uranium is what is left over after natural uranium has been processed to extract 'enriched' uranium. This processing reduces the concentration of the uranium isotope 235 from about 0.7% to 0.2%. U235 is the good stuff as far as nuclear power plant operators and atomic bomb makers are concerned.

The leftover stuff -- mostly U238 -- has a particularly fine property when it comes to tanks: it is amazingly dense. In fact, it's about 1.7 times as dense as lead, so when you're trying to punch a hole through a thick panel of steel, it's quite useful.

As it happens, its density also makes it quite resistant to being punctured, so it also ends up as armour panels in tanks (with steel panels around it to hold it in place).

Do you see the words we've been using here? Density, 6 Pounder, heavier-than-lead.

All of these are anathema to the infantryman, who traditionally expects to carry all his daily needs on his back -- including his weapons and ammunition. It would be asking a little much to expect him to lug around the 3+ kilogram shells of a 6-Pounder, not to mention the thousand kilogram gun to fire it.

Fortunately for him, just before WWII those clever Swiss, who were smart enough to stay out of the fighting itself, reminded the world of the 'shaped charge'. This is simply a carefully designed piece of high explosive designed to focus most of its energy at one precise point. That's what 'shaped' means.

So over the next few years the various combatants developed several versions of the HEAT round. HEAT does not mean that things are hot. Instead it stands for High Explosive Anti-Tank.

Remember, in a sense, anti-tank artillery was a bit like 18th century ship cannons: they punched holes in the sides of their opponents. They didn't actually blow anything up.

But HEAT rounds meant that you could dispense with the weight conventionally required to punch holes in armour. A HEAT round has its shaped charge created with a cavity at one end. As it explodes, the resulting gases punch at up to 50,000 kilometres per hour at a single point. This doesn't melt the armour (that takes too long). Instead it instantly turns it into a state of 'superplasticity', where the metal grains individually slide over each other.

A hole is created in the material upon which the shaped charge is focused. This hole can be quite deep. Typically its depth is about double the diameter of the shaped sharge itself.

One of the more popular antitank weapons is the 84mm Carl Gustav recoilless rifle, designed by the Swedish in 1948 (they, also, were neutral during WW2). A recoilless rifle avoids the recoil by using a rocket rather than a regular cartridge. That means it's a good idea not to stand behind a Carl Gustav when it is fired, since you would be badly hurt by its rocket ignition.

Since the Carl Gustav doesn't actually have to contain the energies of the launching rocket, it can be very much lighter than its size (84mm) implies. Yet it can punch through the side of a tank, thanks to the shaped charge in its HEAT round. Or, indeed, at the start of the Falklands War, one was used by the Royal Marines to sent the Argentine naval corvette, the Guerrico, packing.

Oh, I forgot to mention what happens once the armour of a tank has been penetrated. The tank is disabled, perhaps, by the damaging of sensitive controls within. More reliably, the tank is disabled by the killing of its crew, who are subjected to an unpleasant bathing in high velocity, high temperature metallic gasses.

© 2002-2009, Stephen Dawson