declared that one group of tanks would accompany infantry in a similar role to World War I, while another group of 'cruiser' tanks would then exploit a breakthrough, in a role similar to light cavalry. In the USSR, 1930s tank doctrine specified three groups of tanks: one 'breakthrough' tank in the infantry support role, one tactical breakthrough tank to clear the combat area, and a 'fast tank' for operational maneuver. In Germany, the ideas of Heinz Guderian established the need for unified tank formations, but with a mixture of armaments for differing roles. In the United States, doctrine evolved so that the main purpose of the tank was to provide infantry support and exploitation of breakthroughs. The antitank role was given to tank destroyers. There was no analog to the cruiser tank in pre-war US doctrine. There were those within the US Army which advocated a more modern force with tanks in the cavalry role, but their suggestions were not put into place by the time of the US's entry into World War II. Infantry tank The idea for this tank was developed during World War I by the British and French. The infantry tank was designed to work in concert with infantry in the assault, moving mostly at a walking pace, which required it to carry heavy armour to survive defensive fire. Its main purpose would have been to clear the battlefield of obstacles, suppress or destroy defenders, and protect the infantry on their advance into and through enemy lines by giving mobile overwatch and cover. The British came back to the concept in the pre-Second World War era. The infantry tank did not need to be fast so it could carry more armour. One of the best-known infantry tanks was the Matilda II of World War II. Cruiser tank A cruiser tank, or cavalry tank, was designed to move fast and exploit penetrations of the enemy front. The idea originated in "Plan 1919", a British plan to break the trench deadlock of World War I in part via the use of high-speed tanks. This concept was later implemented in the "fast tanks" pioneered by J. Walter Christie. They were used by the United Kingdom during World War II. Cruiser tanks were designed to complement infantry tanks, exploiting gains made by the latter to attack and disrupt the enemy rear areas. In order to give them the required speed,