Reactive Armour - Explosive Reactive Armor

Explosive Reactive Armor

An element of explosive reactive armor 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 long rod penetrator, the projected plates serve to deflect and break up the rod.

The disruption is attributed to two mechanisms. 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 significantly increases the effective plate thickness during the impact.

To be effective against kinetic energy projectiles, ERA must use much thicker and heavier plates and a correspondingly thicker explosive layer. Such "heavy ERA," such as the Soviet-developed Kontakt-5, can break apart a penetrating rod that is longer than the ERA is deep, again significantly reducing penetration capability.

An important aspect of ERA is the brisance, or detonation speed of its explosive element. ERA was first developed to counter HEAT warheads; which used a shaped charge to create an ultra-high velocity jet of molten metal. The jet's effectiveness derives more from its momentum than its temperature, so the impacting jet must be disrupted quickly as the heat-sink effect of the armour cannot be relied upon.

ERA also counters explosively forged projectiles, as produced by a shaped charge. The counter-explosion must disrupt the incoming projectile so that its momentum is distributed in all directions rather than towards the target, greatly diminishing its effectiveness.

Explosive reactive armor 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. The U.S. Army uses reactive armor on its Abrams tanks as part of the TUSK (Tank Urban Survivability Kit) package and on Bradley vehicles and the Israelis use it frequently on their American built M-60 tanks.

ERA tiles are used as add-on (or "appliqué") armor to the portions of an armored fighting vehicle that are most likely to be hit, typically the front (glacis) of the hull and the front and sides of the turret. Their use requires that the vehicle itself be fairly heavily armored to protect the vehicle and its crew from the exploding ERA;.

A further complication to the use of ERA is the inherent danger to anybody near the tank when a plate detonates (disregarding that a HEAT warhead explosion would already present a great danger to anybody near the tank). 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 cause explosive fragmentation of 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. As a result, infantry needs to operate some distance from vehicles protected by ERA in combined arms operations.