| BT-7, BT-7M | |
|---|---|
 BT-7M, 1940, with tracks removed from the wheels and carried on the hull | |
| Type | Lightcavalry tank |
| Place of origin |  Soviet Union |
| Service history | |
| In service | 1935–45 |
| Used by | Soviet Union Mongolia Finland (captured) Hungary (captured) Romania (captured) Nazi Germany (captured) |
| Wars | Soviet–Japanese Border Wars World War II Winter War Continuation war Soviet–Japanese War |
| Production history | |
| Designer | Morozov |
| Designed | 1935[1] |
| Manufacturer | KhPZ |
| Produced | 1935–40 |
| No. built | 5753[a] |
| Variants | BT-7A, BT-7M (BT-8), BT-IS[1] |
| Specifications (BT-7 model 1937[1]) | |
| Mass | 13.9 tonnes (13.7 long tons; 15.3 short tons) |
| Length | 5.66 m (18 ft 7 in) |
| Width | 2.29 m (7 ft 6 in) |
| Height | 2.42 m (7 ft 11 in) |
| Crew | 3 (commander, loader, driver) |
| Armour | Hull: 6–40 mm Turret: 10–15 mm |
Main armament | 45 mm anti-tank gun M1932/38 (20-K) |
Secondary armament | 2 x 7.62 mmDT machine gun |
| Engine | Mikulin M-17T (V-12) gasoline 450 hp (340 kW) at 1,750 rpm |
| Power/weight | 32.37 hp/tonne |
| Transmission | Chain drive (tracks:sliding gear) |
| Suspension | Christie |
| Ground clearance | 0.305 m (10 in) |
| Fuel capacity | 620 litres (160 US gal) |
Operational range | Road: 250 km (160 mi) Off-road: 120 km (75 mi) |
| Maximum speed | Road: 72–86 km/h (45–53 mph) Off-road: 50 km/h (31 mph) |
Steering system | steering stick |
TheBT-7[b] was the last of theBT series ofSovietcavalry tanks that were produced in large numbers between 1935 and 1940. It was lightly armoured, but reasonably well-armed for the time, and had much better mobility than other contemporary tank designs. The BT tanks were known by the nicknameBetka from theacronym, or its diminutive,Betushka.[2]
The BT-7's successor was the famousT-34 medium tank, introduced in 1940, which replaced all of the Soviet fast tanks,infantry tanks, and medium tanks then in service.
The first prototypes of the BT-7 had a distinctive canted-ellipse shaped turret mounting both the main gun and a coaxialmachine-gun. The specification also called for the project to allow for the installation of new guns without any significant change to the framework: the 76 mm KT-26 or PS-3 main gun (a short-barreled howitzer) and the45 mm 20K model 1932/38, a long-barreled, high-velocity gun useful against tanks, but less effective than the 76 mm gun against infantry.
In the rear of the turret, there was a rotating drum-type magazine for 18 45 mm shells or a radio station. The prototype underwent an 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 theBT-5. (However, the idea of a 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 theT-26-4.) In the production model, a cylindrical turret housed a 45 mm 20K gun with aDT 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. The 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, 153 BT-7Aartillery tanks were produced between 1936 and 1938. 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).
In 1938, four experimental BT-8 tanks mounted withV-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. The diesel tanks were more fuel efficient, and the petrol-powered tanks were soon placed into reserve.
Several experimental tanks were conceived based on the BT series, for example the wheeled BT-IS, designed by N.F. Tsyganov, a platoon commander in the 4th Armoured Regiment of theUkraine Military District and self-taught designer. The type successfully passed field tests, but was not ordered in bulk. Another Tsyganov design was the SV-2 "Cherepakha"(turtle, черепаха), with a new design of hull and turret. There was also the command tank KBT-7 with a fixed superstructure, the OT-7 mounting aflamethrower, the KhBT-7 designed to protect from toxic contamination and lay smokescreens, the SBTbridgelayer and the TTBT-7 and Thubten-7 radio-controlled tanks (known at the time asTeletanks). Finland converted 18 captured tanks intoBT-42 assault guns.[3]
Shortly beforeOperation Barbarossa (the German invasion of the Soviet Union), the BT-7 underwent an up-armoring program. In 1940, theIlyich Iron and Steel Works inMariupol produced 50 sets of hinged homogeneous armor for the BT-7M, which increased the weight of the test tank to 18 tons. Unfortunately, nothing is known about the installation of these kits to military units.
Between 1935 and 1940, 5753 BT-7 tanks of all modifications were built.
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In June 1941, at the outset of Barbarossa, the BT-7 was used as the main cavalry tank of the Soviet army. Tank losses were high, with over 2,000 BT-7 series tanks lost in the first 12 months on theEastern Front. 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.
By 1 November 1942, 32 BT-7 tanks were captured by Romanian forces.[4] BT-7 series tanks continued in use by the Soviets in the Far East, against Japanese forces which lacked the heavy tanks of their German allies. BT-7 tanks were employed against Japanese forces in theBattles of Khalkhin Gol in 1939 and theManchurian Strategic Offensive Operation in 1945.
Although many BT-7 tanks were produced, as of early 2018, there is only one known remaining BT-7 in operational order, in Belarus.[5]
TheTable of Organization and Equipment for a typical Soviet light tank brigade in 1939 is as follows:
