In 1939, the most numerous Soviet tank models were the T-26 infantry tank and the BT series of fast tanks. The T-26 was slow-moving, designed to keep pace with infantry on the ground. The BT tanks were cavalry tanks : fast-moving and light, designed for maneuver warfare. Both were Soviet developments of foreign designs from the early 1930s; the T-26 was based on the British Vickers 6-Ton , and the BT tanks were based on a design from American engineer J. Walter Christie . 
Developed at the same time and closely related to the T29, the T30 Heavy Tank was virtually identical, but was mounted with the 155 mm gun T7, featured a more powerful engine, an had an additional crew member to help load the gun.