As a result of this testing, it was felt that a machine-gun was unnecessary on a tank with a 3-man crew, especially as it made the assembly of the turret more complicated.

These were fitted with a larger turret and a 76 mm KT-type gun with 50 rounds of ammunition (40 in a tank with a portable radio).

After comparative tests of the BT-7 and BT-8, the diesel tanks were put into production in 1940 (under the designation BT-7M) with the powerplants being produced in a separate plant of the Voroshilovets factory to ensure supply.

[3] Shortly before Operation Barbarossa (the German invasion of the Soviet Union), the BT-7 underwent an up-armoring program.

In 1940, the Ilyich Iron and Steel Works in Mariupol produced 50 sets of hinged homogeneous armor for the BT-7M, which increased the weight of the test tank to 18 tons.

Hundreds more had been immobilized before the invasion by poor maintenance, and these had to be abandoned as the Soviet forces withdrew eastward.

The BT-7 continued to be operated by the armored and mechanized forces of the Red Army for almost the entire war, but in greatly-decreased numbers after 1941.

BT-7 tanks were employed against Japanese forces in the Battles of Khalkhin Gol in 1939 and the Manchurian Strategic Offensive Operation in 1945.