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.
Tanks in World War II
The most important American design of the war was the M4 Medium Tank, or "Sherman" in British service. The M4 Medium became the second-most-produced tank of World War II, and was the only tank to be used by virtually all Allied forces (thanks to the American lend-lease program); approximately 40,000 M4 Mediums were produced during the war. M4s formed the main tank of American, British, Canadian, French, Polish and Chinese units. The M4 was the equal of the German medium tanks, the Panzer III and Panzer IV, at the time it first saw service in 1942. The Red Army was supplied with about 4,000 M4s. The M4, although reliable and easy to maintain, was already outgunned by the time the US encountered the up-gunned and up-armored German medium tanks in Italy and Northern Europe (the Panzer IV and various German self-propelled guns) and by late 1943 the arrival of German Panther and Tiger I were even graver threats due to the range, accuracy and penetrating power of their main guns. While it is commonly believed that the Sherman had a tendency to explode catastrophically due to their use of petrol fuel, this is incorrect (almost all tanks used petrol in WWII, excepting Soviet tanks). The Sherman suffered from poor ammunition storage. Welded-on appliqué armor and water jackets were added to combat the problem. A U.S. Army study in 1945 concluded that 60–80 percent of the older dry-stowage and 10–15 percent of wet-stowage Shermans burned when penetrated. The Sherman gained grim nicknames such as "Tommycooker" from the Germans, who called British soldiers "Tommies".