Reactive armour

Content sourced from Wikipedia, licensed under CC BY-SA 3.0.

Reactive armour is a type of vehicle armour that adds a special layer to defend tanks and other armored vehicles from anti-tank weapons. The most common form is explosive reactive armour (ERA). Other types include self-limiting ERA (SLERA), non-energetic reactive armour (NERA), non-explosive reactive armour (NxRA), and electric armour.

How it works
When a shaped-charge warhead hits ERA, the explosive in the layer explodes and pushes the outer plates apart. This disrupts the jet created by the warhead and makes it harder for the penetrator to strike effectively. There are two main effects: the moving plates change the jet’s angle and speed, and as the plates flare out, the jet hits fresh armour, increasing the effective thickness.

ERA is heavier and thicker if it must defend against kinetic energy penetrators. Stronger, faster explosives and plates give more protection, but ERAs have limits.

Tandem charges and weaknesses
Tandem-charge weapons use two charges in quick succession to defeat ERA by detonating it early. This is a common way to defeat older ERA systems. ERA is also less effective against modern armor-piercing fin-stabilized discarding sabot (APFSDS) rounds that use long, hard penetrators.

NERA, NxRA and safety perks
NERA and NxRA use a non-explosive, inert layer between plates. When hit, the plates bulge and the impact point moves, increasing the effective thickness much like ERA, but without using an explosive. These systems can often withstand multiple hits and are safer for nearby soldiers. They cannot be defeated by tandem charges the way explosive ERA can.

Electric armour
Electric or electromagnetic armour uses plates that form a high-energy capacitor. If a penetrator breaches the armor, the circuit dumps energy into the intruding object, potentially vaporizing or turning it into plasma. This technology had not been deployed on real vehicles as of the mid-2000s, and it’s not clear which threats it would guard against.

Usage and handling
ERA is typically added as armor tiles on the front of a vehicle or other areas likely to be hit. While effective, ERA can explode outward and pose danger to nearby troops, so its use requires caution and planning in combat.

History in brief
Ideas about countering hollow charges appeared in the 1940s. Real defensive use began later, with widespread adoption in the late 20th century. Israel first deployed a form of reactive armour on its tanks in the early 1980s, and many other nations followed, making ERA and its variants common on modern tanks.