Tanks were an important weapons system in World War II. Although tanks were the subject of widespread research in the inter-war years, production was limited to relatively small numbers in a few countries. However, during World War II most armies employed tanks, and production levels reached thousands each month. Tank usage, doctrine and production varied widely among the combatant nations. By war's end, a consensus was emerging regarding tank doctrine and design.
The tank was invented by the British in World War I, with nearly simultaneous development in France. Tanks of the First World War reflected the novelty of the idea and the primitive state of the automotive industry. World War I tanks moved at a walking pace, were relatively unreliable, and were employed according to doctrines still being worked out at war's end. A breakthrough in tank design was the Christie suspension: a suspension system developed by American engineer J. Walter Christie which allowed considerably longer movement than conventional leaf spring systems then in common use, which allowed the tanks to have considerably greater cross-country speed.
The doctrine of armored warfare changed radically in the inter-war years as armies sought ways to avoid the deadlock imposed by modern firepower and looked for the means to restore offensive power on the battlefield. Initially, tanks had been used for close support of infantry, but as modern mechanized doctrine was developed by several Armies, tanks became an essential part of the combined-arms team. In addition to infantry support, tanks fulfilled traditional cavalry roles, provided mobile artillery support, and were adapted to combat engineering roles.
Tank design gradually improved in the inter-war period also. Reflecting the growth of the automotive industry, tank engines, transmissions, and track systems were improved. By the beginning of the war in September 1939, tanks were available that could travel hundreds of miles on their tracks with a limited number of breakdowns.
The war accelerated the pace of change in design. In particular, the gun-vs-armor race of the war led to rapid improvements in firepower and armor (both in thickness and design)... (more information at: http://en.wikipedia.org/)