Kinetic energy penetrator

A kinetic energy penetrator is a type of ammunition which uses kinetic energy as the primary means of penetrating armour. Ammunition of this kind lacks explosive, so in order to successfully penetrate modern armour, the round must travel at a high velocity and the force of impact must be concentrated to a small area. These requirements have led to the round commonly being shaped as a long sleek rod.

To produce very high speeds the ammunition is normally composed of a narrow penetrator surrounded by a sabot which expands the diameter to the full barrel width of the firing gun. This allows the pressure of the propellant gasses to act on the full size base and produce rapid acceleration of the round, which is lighter than a full metal round of the same diameter would be. Once the round leaves the barrel the sabot falls off, leaving the penetrator travelling at high speed and with a smaller cross-sectional area, which reduces aerodynamic drag during the flight to the target. This technique was first used in anti-tank guns during World War 2.

KE-penetrators for tanks are commonly just 2-3 centimeters in diameter, and 50-60 centimeters long. To maximize the amount of kinetic energy released on the target, the penetrator must be made of an hard and heavy material, such as tungsten or depleted uranium. If the penetrator was in a soft material such as lead it would flatten out on impact, and most of its kinetic energy would be dissipated as heat on hitting the hard armor and no effective penetration would happen.

Because a long, thin rod is aerodynamically unstable and tends to tumble in flight, two different approaches have been used to stabilise them. The oldest is rifling, which spins the round. This is the technique generally used in British guns until the 1980s. An alternative approach is to add fins like those of an arrow to the base and fire the round from a smooth bore gun. This is the approach commonly used in recent Russian, German and US guns (the British now use a locally produced licensed copy of the same German 120mm smoothbore gun as the US does). Sometimes a rifled barrel has been combined with fin stabilisation, using some system to prevent the round from spinning in the barrel. The rifled barrel approach improves the accuracy of the other types of ammunition which must be fired.

Other names for KE-penetrators include APFSDS (Armour Piercing Fin Stabilized Discarding Sabot) and long-rod penetrator. It is generally accepted that KE-penetrators are the most effective ammunition in penetrating armour today.

A typical rifle bullet is also a kinetic energy penetrator when faced with either body armour or lightly armoured vehicles and there have at times been moves to use the sabot and thin penetrator approach in rifle ammunition, either to lower the weight of the round or to increase penetration. These attempts have generally been less successful than conventional rounds for other target types and have not replaced them as general purpose ammunition.