BT tank

BT-2, BT-5, BT-7, BT-7M
BT-7
Type	Light cavalry tank
Place of origin	Soviet Union
Service history
In service	1932–45
Wars	Spanish Civil War, Second Sino–Japanese War, Soviet–Japanese border conflicts, Winter War, World War II
Production history
Designer	J. Walter Christie, Kharkiv Morozov Machine Building Design Bureau (KMDB)
Designed	1930–31
Manufacturer	Malyshev Factory
Produced	1932–41
No. built	BT-2: 650 BT-5: 1884 BT-7: 5556
Variants	BT-2, BT-5, BT-7, BT-7M
Specifications (BT-5)
Weight	11.5 tonnes (12.676 tons)
Length	5.58 m (18 ft 4 in)
Width	2.23 m (7 ft 4 in)
Height	2.25 m (7 ft 5 in)
Crew	3
Armour	6–13 mm
Main armament	45-mm Model 32 tank gun
Secondary armament	7.62-mm DT machine gun
Engine	Model M-5 400 hp (298 kW)
Power/weight	35 hp/tonne
Suspension	Christie
Fuel capacity	360 litres (95 US gal)
Operational range	200 km (120 mi)
Speed	72 km/h (44.7 mph)

The BT tanks (Russian: Быстроходный танк (БТ), Bystrokhodny tank, lit. "fast moving tank" or "high-speed tank") were a series of Soviet light tanks produced in large numbers between 1932 and 1941. They were lightly armoured, but reasonably well-armed for their time, and had the best mobility of all contemporary tanks in the world at that time. The BT tanks were known by the nickname Betka from the acronym, or its diminutive Betushka. The successor of the BT tanks 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 in service.

The BT tanks were "convertible tanks". This was a feature designed by J. Walter Christie to reduce wear of the unreliable tank tracks of the 1930s. In about thirty minutes, the crew could remove the tracks and engage a chain drive to the rearmost road wheel on each side, allowing the tank to travel at very high speeds on roads. In wheeled mode, the tank was steered by pivoting the front road wheels. Soviet tank forces soon found the convertible option of little practical use; in a country with few paved roads, it consumed space and added needless complexity and weight. The feature was dropped from later Soviet designs.

Christie, a race car mechanic and driver from New Jersey, had failed to convince the U.S. Army Ordnance Bureau to adopt his Christie tank design. In 1930, Soviet agents at Amtorg, ostensibly a Soviet trade organization, used their New York political contacts to persuade U.S. military and civilian officials to provide plans and specifications of the Christie tank to the Soviet Union. At least two of Christie's M1931 tanks (without turrets) were later purchased in the United States and sent to the Soviet Union under false documentation, in which they were described as "agricultural tractors". Both tanks were delivered to the Kharkov Komintern Locomotive Plant (KhPZ). The original Christie tanks were designated fast tanks by the Soviets, abbreviated to BT (later referred to as BT-1). Based both on them and on other plans obtained earlier, three unarmed BT-2 prototypes were completed in October 1931 and mass production began in 1932. Most BT-2s were equipped with a 37 mm gun and a machine gun, but a shortage of 37 mm guns led to some early examples being fitted with three machine guns. The sloping front hull (glacis plate) armor design of the Christie M1931 prototype was retained in later Soviet tank hull designs, later adopted for side armor as well. The BT-5 and later models were equipped with a 45 mm gun.