Essentially all anti-tank munitions work by piercing the armor and killing the crew inside. Reactive armor's protective mechanism involves producing an explosion or other such reaction when it is impacted by a weapon, actively "pushing back" against it. This is particularly effective against shaped charge warheads, in which the warhead directs a focused jet of molten metal against the armor; reactive armor's reaction disrupts the jet before it reaches the armor's surface.
The effect was discovered in 1967–68 by a German researcher, Manfred Held, working in Israel. He and his team were using the large quantities of wrecked tanks from the Six Day War to test shells. They accidentally discovered that tanks that still contained live ordinance could disrupt a shaped charge by the explosion of the shells, the basis of ERA. The concept was patented in 1970."
I am grateful to Israel for their help on behalf of United States soldies. It just appears that the Army was a little slow on the uptake in getting this type of technology in place. There may be any number of explanations of course, budget cuts, cold war drawdown, but still, I wonder.
ERA is yet another example of a military technology developed in order to neutralise a disadvantage rather than take it head on.It's much like how the Russians developed supersonic anti-ship missiles after realising that their targetting & ECCM systems were never going to match Western standards.The same logic is evident in ERA systems which the Russians have developed for most of their tanks including T-62s.A lot of countries are developing or have developed ERA systems including the US,but Israel & Russia have been the most energetic about it & for obvious reasons.
M-1 Abrams Tank Proves Useful, Vulnerable In Iraq
(Washington Times, March 31, 2005, Pg. 9)
The Army's M1 Abrams tank unexpectedly has proven to be one of the best weapons in close-range urban warfighting in Iraq, but its once invincible image has been shattered by an inventive enemy. Insurgents have destroyed more than 20 of the 68-ton armored fortresses and disabled scores more, not with sophisticated anti-tank weapons, but with relatively crude rocket-propelled grenades and roadside bombs.