Panzer VIII Maus
Panzerkampfwagen VIII Maus ("Mouse") was a German World War II super-heavy tank completed in late 1944. It is the heaviest fully enclosed armoured fighting vehicle ever built. Five were ordered, but only two hulls and one turret were completed before the testing grounds were captured by advancing Soviet military forces.
History of the tank
The United States had even more reason to standardize and mass-produce than did the Soviet Union. By concentrating on mechanical reliability, the US was able to produce vehicles that operated longer with fewer repair parts. To ensure that American tanks were compatible with American bridging equipment, the War Department restricted tank width and maximum weight to thirty tons. The army relaxed these requirements only in late 1944.