Our distant ancestors quickly learned that if you take something heavy and throw it very fast it can cause a great deal of damage to a foe. Goliath, for example. The gift of kinetic energy has given to warfare many devices that try to increase the mass or velocity in the expression for kinetic energy. Of course, since the velocity is squared, much more is gained from focusing on an increase in speed rather than an increase in mass, but when they both are large a great deal of havoc can be achieved. 

Modern armored vehicles have many lethal threats, from slow-moving Unmanned Aerial Vehicles ( UAVs) dropping munitions to fast anti-tank guided missiles, but the winner of the kinetic energy threat is the kinetic energy penetrator, or KEP. A KEP is typically a rod of a dense material, often tungsten, which is typically fired from an autocannon. The rod is pointed, which assists in penetration, and the metal is often treated to have a “self-sharpening” effect through manipulation of the grain structure in the metal or the use of composites to form layers that are sloughed off. Full penetration of the armor creates shrapnel and heat inside the vehicle, rendering the crew and equipment non-functional, even with very thick armor (the M1 Abrams has up to 700 mm equivalent of rolled homogeneous armor), which a KEP can penetrate. The tungsten rod has tail fins to help it maintain stability in flight and a perpendicular orientation on contact with the target. In the cannon it’s surrounded by a lightweight sabot (French for clog, a type of shoe) that fills the chamber and barrel to take the full pressure of the propellant ignition but separates from the KEP round soon after the assembly leaves the muzzle. A typical KEP has a mass of 6.2 kg and a muzzle velocity of 1,560 m/s, which leads to a muzzle energy of over 15 megajoules. In comparison, a .30-06 rifle round, which is considered ample for big game, has a muzzle energy of only 3.6 kilojoules. Anti-tank rifle rounds on the order of 20 mm caliber achieve about 6 MJ at the muzzle. The figure shows a 30 X 173 mm armor piercing fin stabilized discarding sabot-tracer (APFSDS-T) round that can be used in a 30-mm NATO autocannon. For scale, it’s 290 mm long.

Countermeasures against such a small, heavy, fast-moving threat are limited, but they consist of slowing the projectile with metal grids or skirts, deflecting the projectile by explosions from reactive armor, using layered or moveable armor to reduce momentum or fragment the rod, or intercepting the round with explosively-propelled metal plates. In the case of lightly-armored vehicles such as the Bradley AFV, a KEP can prove quite devastating, hence the development of active protection systems with radar/electro-optic sensing, classification, and automatic countermeasure deployment.