BT tanks in 30th years made a basis of tank formation of Red Army. To the beginning of the Second World War it was produced about 7500 of this tanks (more than 5000 of BT-7 different modifications). Tank BT-7 is differed from the previous models by a design of the body, the new engine and a number of other changes. In 1937 the new conic welded tower specially for tank BT-7 was developed.