Background
During World War Two, the Allies encountered German tanks with heavier armor and more powerful guns than those the Allies possessed. The US initiated development and testing of heavy tanks in 1943 as the armor on the M26 was not thick enough to stand against the latest German guns. The war ended before the US Army could deploy a heavy tank in Europe, but a need was recognized for a heavy tank to counter the deployment of the IS-3 by the USSR. The T43, mounting a 120mm main gun and a new V-12 engine was selected as the new heavy tank. The T43 became the basis for the M103, America's only operational heavy tank.