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
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 1935:
BT-7 Model 1937 A new tower with angled armor
- BT-7A: the BT-7A is a version of the BT-7 with only machine guns
- BT-7TU - Command version with a frame antenna, later replaced by the less conspicuous whip antenna
- ChBT-7 - version designed for spraying chemicals, poisoning, decontamination and creating smoke screens
- CBT-7 command a tank with a fixed tower
- OT-7 (огнемётный танк) plamenometná version of the armored tanks of flammable substances on the left side of the bucket
- BT-7M also known as BT-8
- BT-42 Finnish version made by captured BT-7A with a mounted British 114 mm howitzer
- Model: BT -7
- Garrison: three men (commander / gunner, driver and municipal )
- Length: 5.66 m
- Width: 2.29 m
- Height: 2.42 m
- Weight13.8 tonnes
- Engine: M17T, 12-cylinder, gasoline, water cooled (450 hp)
- Speed: 53 km / h ( road, about caterpillars) or 73 km / h ( road on wheels)
- Range: 375 km (worms) or 500 km ( wheels)
- Hoof Shield: 13–22 mm ( front), 13mm ( side and stern ), 10 mm (roof) and 6–10 mm ( bottom)
- Tower Shield: 15 mm (front, side and aft ) and 10 mm (roof)
- Main Armament: 1934 M Cannon 45 mm/L46
- Secondary armament: 2-3 7.62 mm DT machine gun (coaxial, hull and back of the tower, last 2 optional )
- Ammunition: 132-188 45 mm grenades and 2394 rounds of 7.62 mm
- ↑ Zaloga 1984, p 74.
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