reactive armour - Explosive reactive armour, Non-explosive and non-energetic reactive armour, Electric reactive armour

A form of protection for military vehicles such as tanks against the kind of ‘hollow-charge’ warhead typically used in infantry-fired antitank missiles; developed in Chobham, Surrey, it is also known as Chobham armour. This warhead is designed to burn its way through the armoured metal skin of the vehicle in a hot jet of gas and molten metal, rather than to smash its way in using simple kinetic energy. On impact from such a hollow-charge weapon, reactive armour itself detonates locally, neutralizing the attacking weapon's effects.

Reactive armour is a type of vehicle armour that reacts in some way to the impact of a weapon to reduce the damage done to the vehicle being protected. The most common type is explosive reactive armour (ERA), but variants include self-limiting explosive reactive armour (SLERA), non-energetic reactive armour (NERA), non-explosive reactive armour (NxRA), and electric reactive armour.

Explosive reactive armour

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. First, the moving plates change the effective velocity and angle of impact of the shaped charge jet, reducing the angle of incidence and increasing the effective jet velocity versus the plate element. Second, since the plates are angled compared to the usual impact direction of shaped charge warheads, as the plates move outwards the impact point on the plate moves over time, requiring the jet to cut through fresh plate material. This second effect increases the effective plate thickness during the impact significantly.

To be effective against kinetic energy projectiles, ERA must use much thicker and heavier plates and a correspondingly thicker explosive layer.

Explosive reactive armour has been valued by the Soviet Union and its now-independent component states since the 1980s, and almost every tank in the eastern-European military inventory today has either been manufactured to use ERA or had ERA tiles added to it, including even the T-55 and T-62 tanks built forty to fifty years ago, but still used today by reserve units.

ERA tiles are used as add-on (or "appliqué") armour to the portions of an armoured fighting vehicle that are most likely to be hit, typically the front (glacis) of the hull and the front and sides of the turret.

A further complication to the use of ERA is the inherent danger to anybody near the tank when a plate detonates. Although ERA plates are intended only to bulge following detonation, the combined energy of the ERA explosive, coupled with the kinetic or explosive energy of the projectile, will frequently explosively fragment the plate. The explosion of an ERA plate creates a significant amount of shrapnel, and bystanders are in grave danger of serious or fatal injury.

Non-explosive and non-energetic reactive armour

NERA and NxRA operate similarly to explosive reactive armour, but without the explosive liner. When struck by a shaped charge's metal jet, some of the impact energy is dissipated into the inert liner layer, and the resulting high pressure causes a localized bending or bulging of the plates in the area of the impact. As the plates bulge, the point of jet impact shifts with the plate bulging, increasing the effective thickness of the armour. This is almost the same mechanism as the second mechanism that explosive reactive armour uses, but it uses energy from the shaped charge jet rather than an explosive.

Since the inner liner is not explosive itself, the bulging is less energetic than on explosive reactive armour.

Electric reactive armour

A new technology of electric reactive armour is in development, where the armour is made up of two or more conductive plates separated by some space or by an insulating material, creating a high-power capacitor.