http://www.globalsecurity.org/military/systems/munitions/at4.htm
The M136 AT4 is the Army's primary light anti-tank weapon. The M136 AT4 is a recoilless rifle used primarily by Infantry Forces for engagement and defeat of light armor. The recoilless rifle design permits accurate delivery of an 84mm High Explosive Anti-Armor warhead, with negligible recoil.