Reactive armor

"Reactive armor' is a family of materials intended to protect armored fighting vehicles from the effects of certain antitank weapons, especially shaped charges. It is generally considered a Russian invention, although there are some claims of earlier British experiments; a second generation was designed by Israel.

Reactive armor is counterintuitive, in that it protects the tank or other vehicle by covering it with explosives. The explosives, however, are layered on top of the conventional passive armor. When struck by a shaped charge, which must explode at a precise standoff distance, the explosion of the reactive armor either knocks the charge away, or disrupts its stream of molten metal. Kinetic-energy long-rod penetrators, which are extremely hard but brittle, also can be disrupted.

Some of the disadvantages of reactive armor is that it produces fragments hazardous to friendly infantry, especially in urban combat. The individual reactive armor plates are usable once, and then must be replaced.