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.
Bob Semple tank
Due to the limitations of requirements and resources, the tank was a functional failure. By using a large tractor as a base, and bolting on a hastily designed and poorly constructed tank superstructure, the resultant tanks were inadequately armored, extremely heavy (20–25 ton), unstable, restricted by tractor gearing to slow speeds, and had to stop to change gears. Furthermore, due to the shape of the underlying tractor and undue vibrations, shooting from the tank was both difficult and inevitably inaccurate. The use of all these impractical designs had often caused the Bob Semple Tank to be regarded as "The worst tank ever built"