Reactive armour
When a shaped charge strikes the upper plate of the armour, it detonates the inner explosive, releasing blunt damage that the tank can absorb.
Reactive armour 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.
The Australians were the first recorded to have conceptualized and developed methods to disrupt and spread the jet of a hollow charge shell to reduce its penetrating power.
The destructive effect of the shaped charge was identified as caused by a jet moving at high velocities, consisting of particles from the liner.
[1] [2] The idea of counterexplosion (kontrvzryv in Russian) in armour was proposed in the USSR by the Scientific Research Institute of Steel (NII Stali) in 1949 by academician Bogdan Vjacheslavovich Voitsekhovsky.
[citation needed] For a number of reasons, including the aforementioned accident and a belief that Soviet tanks had sufficient armour, the research was ended.
No more research was conducted until 1974, when the Ministry of the Defensive Industry announced a contest to find the best tank protection [citation needed].
Picatinny Arsenal, an American military research and manufacturing facility experimented with testing linear cutting charges against anti-tank ammunition in the 1950s, and concluded that they may be effective with an adequate sensing and triggering mechanism, but noted "tactical limitations"; the report was declassified in 1980.
[4] Reactive armour created on the basis of the joint research was first installed on Israeli tanks during the 1982 Lebanon war and was judged very effective.
Such ERA is ineffective against modern armor-piercing fin-stabilized discarding sabot (APFSDS) projectiles, however, due to their depleted uranium construction.
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.
However, computer simulations indicate that a small caliber (30 mm) HEAT projectile will detonate an ERA, as would larger shape charges and APFSDS penetrators.
[8] Since the inner liner is non-explosive, the bulging is less energetic than on explosive reactive armour, and thus offers less protection than a similarly-sized ERA.
However, NERA and NxRA are lighter, safe to handle, and safer for nearby infantry; can theoretically be placed on any part of the vehicle; and can be packaged in multiple spaced layers if needed.
