Hi After the 6 day war in the middle east Israil did tests with reactive armour(History Channel progame),they tried putting explosvies to the outside of the hulls and turrets,they ended up with replacable reactive armour ,looks like small blocks (two plates with explosives between)if an RPG or tank round hits it it blows the incomming round away from the tank,stopping it penatrating the hull or turret,this is not Chobham but reactive armour.See link http://en.wikipedia.org/wiki/Reactive_armour

Hope this helps

regards pete

P.S the first effective armour was in the 20swhen a thin layer of high tensile steel was fitted to the outsideof normal steelto make it bullet proof.