BT - 7 The BT - 7 was the last of a series of Soviet cavalry tank that were produced in large numbers between 1935 and 1940 . They were lightly armoured , but reasonably well - armed for their time , and had much better mobility than other contemporary tank designs . The BT tank s were known by the nickname " Betka " from the acronym , or its diminutive " Betushka " . The successor of the BT - 7 Tank would be the famous T - 34 medium tank , introduced in 1940 , which would replace all of the Soviet fast tanks , infantry tanks , and medium tanks then in service . Using the American Christie suspension , allowing high speed , the BT - 7 was the final development of tanks BT ( BT - 1 BT - 2 BT , BT - S and BT - 5 ) , having , through the experience of combat , welded armor steeper , higher speed and cannon more powerful engine . Several versions of the basic model were developed ( command , flamethrowers and short gun of 76 . 2 mm ) , and BT - 7M ( also known as BT - 8 ) , in 1939 which received increased frontal armor and power engine History . The first prototypes of the BT - 7 had a distinctive canted - ellipse shaped turret mounting both the main gun and a coaxial machine - gun . The specification also called for the project to allow for installation without any significant change to the framework of new guns : the 76mm CT or PS - 3 main gun and the 45mm 20K model 1932 / 38 . In the rear of the turret there was housed a rotating drum - type magazine for 18 76mm shells or a radio station . The prototype underwent extensive testing program in the summer and autumn of 1934 . 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 . Therefore , in early 1935 , the tank went into production with a simpler design , incorporating the turret from the BT - 5 . ( However , the idea of wheeled / tracked vehicle with a 76 - mm cannon was not abandoned and the plant was commissioned to develop a new BT - 7 turret from the turret of the T - 26 - 4 . ) In the production model , a cylindrical turret housed a 40mm 20K gun with a DT - model machine - gun . On some of the tanks , a model 71 - TC radio with frame antenna was installed . The crew consisted of three men : the commander ( who also served as the gunner ) ; the loader and the driver . In 1937 the company launched production of the BT - 7 with a conical turret . Main armament remained the same , but the ammunition was increased to 44 rounds . All serving tanks now installed the DT machine gun in the rear niche . For the firing of the gun and coaxial machine gun at night , the tank was equipped with two special projector - type headlamps , and a mask placed on the gun . Subsequently , these lights were retrofitted to earlier models of the tank . Improvements were also made to the drive wheels , caterpillar tracks and gearbox by 1938 . In parallel with the main modification , 154 artillery tank BT - 7A were produced between 1936 and 1938 , fitted with a larger turret and a CT - type gun , 50 rounds of ammunition ( 40 in a tank with a portable radio ) . In 1938 , four experimental BT - 8 tanks mounted with V - 2 diesel engines were produced . 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 . From December 1939 , the BT - 7A went into production with some minor modifications - additional bracing for rigidity , a manhole underneath , and a smaller air filter . The diesel tanks showed much - reduced fuel costs , and the petrol tanks were soon placed into reserve . Several experimental tanks were conceived based on the BT series , for example the wheeled BT - IC , designed by NF Tsyganova , a platoon commander in the 4th Armoured Regiment of the Ukraine Military District and self - taught designer . The type successfully passed field tests but was not ordered in bulk . Another Tsyganova design was the S - 2 " Turtle " , with a new design of hull and turret . There was also the command tank CBT - 7 with a fixed turret , the OT - 7 mounting a flamethrower , the HBT - 7 designed to protect from toxic contamination and lay smokescreens , the PBT bridgelayer and the TTBT - 7 and Thubten - 7 radio - controlled tanks ( known at the time as " Teletanki " ) . Shortly before Operation Barbarossa , the BT - 7 underwent an up - armour programme . In 1940 , Mariupol Ilyich Iron and Steel Works produced 50 sets of hinged homogeneous armor for the BT - 7M , which increased the weight of the test tank to 18 tons . On the installation of these kits to military units , unfortunately , nothing is known . Between 1935 and 1940 , 5328 BT - 7 tanks of all modifications ( except BT - 7A ) were built . They are operated by the armored and mechanized forces of the Red Army for almost the entire war . They fought against the Wehrmacht until superseded by more modern types in 1944 , but continued in use elsewhere , including being used against Japanese forces ( Battle of Khalkhyn Gol and Manchurian Strategic Offensive Operation ) in Manchuria in 1945 . BT - 7 Model 1937 A new tower with angled armor