Wrapping Up

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Under normal circumstances, the energy from an explosive spreads evenly in all directions.

But if an explosive is given a hollow conical shape and lined with a layer of metal called a shaped-charge liner, the blast forces the energy inward, compressing the liner into an extremely thin, high-temperature metal jet moving at tremendous speed. Its leading edge can reach an astonishing thirty times the speed of sound.

This is the principle commonly used in RPGs and anti-tank missiles: concentrating dispersed explosive energy to penetrate a surface at a single point.

But metal jets have a fatal flaw: at the wrong distance, they are useless.

The optimal standoff distance for a metal-jet warhead-the distance between the point of detonation and the target-is approximately twice its caliber. If the distance is too short, the jet has no time to stretch out; too far, and it breaks apart.

That is why tanks often have a layer of slat armor installed on the outside. Detonating the warhead a short distance early sharply reduces the metal jet's power.

For sensor-fuzed munitions, engineers therefore use an improved version of the shaped-charge warhead: the explosively formed penetrator, or EFP, also commonly called a "self-forging fragment."

By adjusting the liner's shape, the explosive charge, and other design elements, the energy of the explosion can forge the metal liner into a short, thick, high-speed projectile and propel it outward. Its initial velocity is only a third of a metal jet's, but its ability to retain speed and its attack range undergo a qualitative change.

But an EFP projectile is not a precisely machined product. It encounters tremendous drag and is far less stable in flight than