Reactive armour

Reactive armour is a type of vehicle armour used in protecting vehicles, especially modern tanks, against shaped charges and hardened kinetic energy penetrators. 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 armour. NERA and NxRA modules can withstand multiple hits, unlike ERA and SLERA.

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 is intended to counteract anti-tank munitions that work by piercing the armour and then either killing the crew inside, disabling vital mechanical systems, or creating spalling that disables the crew—or all three.

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. Without tandem charges, hitting precisely the same spot twice is much more difficult.

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. In a June 1944 report from the Explosives Manufacturing Practices Laboratory of the Defence Explosive Factory Maribyrnong, an operational requirement for the defence against shaped charges was laid out. The focus was in regard to Japanese 75 mm hollow charge shells used against Allied tanks in the Pacific. The destructive effect of the shaped charge was identified as caused by a jet moving at high velocities, consisting of particles from the liner. The two methods developed were to destroy the jet by forcing it to act through a layer of explosives, disrupting the jet, and to make it act through a layer of oxidiser, destroying the jet by burning it with oxidising agents.

The earliest trials were done with small charges able to defeat 2 inch of steel plate which were readily defeated by a layer of explosive (Baratol, R.D.X., Cordite, etc.) or a vigorous oxidising medium. Subsequent trials with British No.68 and American M9A1 grenades were carried out. However trials were done in few numbers which caused varied results. A mixture of Sodium and Potassium Nitrates explosives was seen as the most practical option due to their casting properties. The mixture acted as an oxidiser which may explode when dispersed and heated. The Explosives Manufacturing Practices Laboratory seemingly developed a more middle road between chemical armor and explosive reactive armor concepts to counter the hollow charge threat.

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. The first pre-production models were produced during the 1960s. However, insufficient theoretical analysis during one of the tests resulted in all of the prototype elements being detonated.^{[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.