Tanks played an important role in World War II. Invented by the British in World War I, the tank gradually improved in the inter-war period and also saw rapid changes in the Second World War.
At one point a tank seemed to be state-of-the-art, then a year later it was obsolete.
Tank doctrine changed radically during WWII. Previously, tanks had been used to support infantry, but with the concept of Blitzkrieg, tanks became a formidable branch of the army in its own right.
Before the end of the war, tanks had superseded infantry as the most important force on the battlefield.