The ancestry of the T-34 derives from the BT series of fast tanks developed in the USSR in the 1930s. These were discovered to be too lightly armoured and armed for the sort of combat that would be expected. The T-34 took the BT's Christie-type suspension and incorporated it into a much more robust tank (The BTs were derived from prototype fast tanks built by American tank designer J. Walter Christie, which were sold to the Soviet Union after the American military declined to buy them. The T-34 incorporates elements of the Christie suspension, in particular the large road wheels).
Development proper commenced in 1936, and a prototype was completed in 1939. Full scale production started in 1940. The T-34 was produced in two major variants, the basic T-34/76 with a 76-mm gun (simply called T-34, in Soviet service), and the T-34/85 with an 85-mm gun.
Between 1940 and 1944 nearly 40,000 T-34/76 tanks were produced.