Reactive armor is a type of vehicle armor that reacts in some way to the impact of a weapon to reduce the damage done to the vehicle being protected. It is most effective in protecting against shaped charges and specially hardened kinetic energy penetrators. The most common type is explosive reactive armor (ERA), but variants include self-limiting explosive reactive armor (SLERA), non-energetic reactive armor (NERA), non-explosive reactive armor (NxRA), and electric reactive armor. Unlike ERA and SLERA, NERA and NxRA modules can withstand multiple hits, but a second hit in exactly the same location will still penetrate.
Essentially all anti-tank munitions work by piercing the armor and killing the crew inside, disabling vital mechanical systems, or both. Reactive armor can be defeated with multiple hits in the same place, as by tandem-charge weapons, which fire two or more shaped charges in rapid succession.
Without tandem charges, hitting the same spot twice is much more difficult. An element of explosive reactive armour consists of a sheet or slab of high explosive sandwiched between two plates, typically metal, called the reactive or dynamic elements.
On attack by a penetrating weapon, the explosive detonates, forcibly driving the metal plates apart to damage the penetrator. Against a shaped charge, the projected plates disrupt the metallic jet penetrator, effectively providing a greater path-length of material to be penetrated. Against a kinetic energy penetrator, the projected plates serve to deflect and break up the rod. compiled by XENOCIDE
