Heavy tank
The Char 2C was one of the largest tanks ever produced. At the start of World War II, France and the Soviet Union were the only countries to have inventories of heavy tanks, such as the Char B1, T-35, and KV-1. The Matilda II was designed under the British infantry tank concept which is similar to the heavy tank having thick armor and weighing more than their other tanks. It’s usually separate because they have less firepower with their cruiser tanks (comparable to mediums) at the time having the same main armament but more machine guns. Later war examples were the German Tiger I and II, as well as the Soviet IS series. Note that "heavy" versus "medium" is more a question of tactical roles than weight; the Panther, for example, was a "medium" tank that outweighed most Allied "heavy" tanks.
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"