The BT 5 tanks was the firs model in the seires to be mass produced. They were all able to go on railroad tracks as well as on roads or in the terrain. With their thin armour they were fast (in Russian 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. The BT 5 model saw just a low production.