The BT tanks were mass produced (c. 7 918) from 1932 to 1941 in basically 4 models who all got thicker armour. They were able to go on railroad tracks as well as on roads or in the terrain. With their thin armour they were fast (BT= Bystrochodnij Tank= fast tank) and meant to be active in large numbers on the battle field and transported there by railroad on their own. A chassis imported from the USA in 1931 was the protoytpe. The last BTs were in action in the winter of 1942-43 in the Leningrad/Karelia front. Production BT 8: 1939 a few, 1940: 706, 1941 a few.