Tanks in World War I
The continued need for four men to drive the tank was solved with the Mark V which used Wilson's epicyclic gearing in 1918. Also in 1918 the French produced the Renault FT, the result of a co-operation between Estienne and Louis Renault. As mentioned before, it had the innovative turret position, and was operated by two men. At just 8 tons it was half the weight of the Medium A "Whippet" but the version with the cannon had more firepower. It was conceived for mass production, and the FT became the most produced tank of World War I by a wide margin, with over 3,000 delivered to the French Army. Large numbers were used by the Americans and several were also lent to the British.
Tank classification
Tank doctrine in the UK 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.