Shaped Charge

A shaped charge is an explosive warhead designed to concentrate its energy along one axis rather than dispersing it in all directions. The principle, known as the Monroe effect or hollow-charge effect, is that a hollow cavity formed in the explosive — typically lined with a thin layer of ductile metal — causes the detonation to collapse that liner inward along the charge's axis. The collapse extrudes the liner into a narrow, extremely fast jet of material traveling at several kilometers per second, followed by a slower slug of the remaining liner.

The jet does not melt through armor; it penetrates by hydrodynamic pressure, pushing material aside at pressures so extreme that both jet and armor behave briefly like fluids. Penetration depth depends on the jet's length and density, which is why warhead diameter and the standoff distance — the gap between the charge and the target at detonation — matter so much to designers. This is also the physics behind spaced armor, slat armor, and explosive reactive armor, all of which exist to disrupt the jet before it reaches the main plate.

Shaped charges dominate drone munitions because they deliver a heavy anti-armor effect from a light warhead: a charge a quadcopter can carry can defeat the roof armor of a main battle tank. The same principle, at larger scale, arms most rocket-propelled grenades and anti-tank guided missiles.