The T-54/55 is a main battle tank that was developed by the Soviet Union in 1947. The most-produced tank in history, it is currently used by 50 armies across the world, mostly former Eastern Bloc nations or Third World countries. 100,000 T-54/55s have been produced, and the United Kingdom developed the Royal Ordnance L7 and the United States the M60 Patton in response to the strength of the T-54/55.