BT tank

The BT tanks (Быстроходный танк (БТ), Bystrokhodny tank, lit. "fast tank") were a series of Soviet cavalry tanks produced in large numbers between 1932 and 1941. They were lightly armoured, but reasonably well-armed for their time, and had much better mobility than other contemporary tank designs. The BT tanks were known by the nickname Betka from the acronym, or its diminutive Betushka.

The direct 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.

Overview
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. However, Soviet tank forces soon found the convertible option of little practical use in a country with few paved roads, and it consumed space and added needless complexity and weight. The feature was dropped from later Soviet designs.

BT tanks saw service in the Spanish Civil War, in the Winter War in Finland, in the Battle of Khalkhin Gol, the Polish campaign, in the early and last days of World War II. The BT tank design served as a platform for experimentation with artillery support tanks and advanced armour layout, and further development led directly to the famous T-34 tank.

Production history


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 on the Christie tank design 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 successfully delivered to the Kharkov Komintern Locomotive Plant (KhPZ). The original Christie tanks were designated fast tanks by the Soviets, abbreviated BT. Based on the Christie prototypes and previously obtained plans, 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 shortages of 37 mm guns led to some early examples being fitted with three machine guns. The BT-5 and later models were equipped with a 45 mm gun. The sloping front armor design of the Christie M1931 prototype was retained in later Soviet tank hull designs, later adopted for side armor as well.

In 1937, a new design team was formed at the KhPZ under Chief designer Mikhail I. Koshkin, to create the next generation of BT tanks. The team built a BT prototype called the A-20, but also built a more heavily armed and armoured derivative, the A-32, a "universal tank" to replace both the T-26 infantry tank and BT cavalry tanks, as well as the T-28 medium tank. The design was controversial, but concerns about tank performance under the threat of German blitzkrieg led to the approval for production of a still more heavily-armoured version, the T-34 medium tank.

Production:
 * BT-2: 620
 * BT-5: 2,108
 * BT-7: 4,965
 * BT-7M: 790

Variants



 * BT-1: Christie prototype with no turret.
 * BT-2 Model 1932: M-5-400 engine (copy of U.S. Liberty engine), three modifications of turret produced: with single 37 mm gun; 37 mm gun and one DT machine gun; twin DP machine guns mount and a single machine gun. In late 1932 modified to BT-3 but produced under same designation.
 * BT-3: same as BT-2, produced according to metric system (instead of Imperial system as used for BT-2). In official documentation referred to as BT-2.
 * BT-4: was a design with welded hull and minor changes in the suspension. 3 prototypes produced (with partially riveted hull)
 * BT-5: larger cylindrical turret, 45 mm gun, coaxial DT machine gun.
 * BT-5 Model 1933: new turret with twin hatches and larger bustle.
 * BT-5PKh: snorkelling variant (prototypes only).
 * BT-5A: artillery support version with 76.2 mm howitzer (few made).
 * BT-5 flamethrower tank: (prototypes only).
 * PT-1A: amphibious variant with new hull (few made).
 * BT-7 Model 1935: welded hull, redesigned hull front, new Mikulin M-17T engine (licensed copy of a BMW engine), enclosed muffler.
 * BT-7 Model 1937: new turret with sloping armour.
 * BT-7TU: command version, with whip antenna instead of earlier frame antenna.
 * BT-7A: artillery support version with 76.2 mm howitzer.
 * OP-7: flame-thrower version with external fuel panniers (prototype only).
 * BT-7M (1938, prototypes designated A-8; sometimes referred to as BT-8): new V-2 diesel engine replacing earlier gasoline engines, three DT machine guns: coaxial, in P-40 AA mount on roof and in a ball-mount on turret rear.
 * BT-42: Finnish assault gun, captured BT-7s were equipped with British 114 mm howitzers.
 * BT-IS: Prototype/proof-of-concept platform with heavily sloped armor; forerunner of the armor design on the T-34.
 * BT-SW-2 Cherepakha ("turtle"): Another prototype, which took the armour sloping to an extreme.
 * A-20: Prototype for a new BT tank, with 20 mm armour, 45mm gun, model V-2 diesel engine, and 8×6-wheel convertible drive. Lost out in trials to the A-32, which was further improved and produced as the T-34 medium tank.


 * TTBT-5, TTBT-7: teletanks, remote-controlled tanks.

Combat history


BT tanks were used in combat on several occasions prior to World War II. A battalion of BT-5s saw action on the Republican side in the Spanish Civil War, where their 45 mm guns could easily destroy the opposing German and Italian light tanks. In the 1939 border skirmishes against Japan (including the battle of Khalkhin Gol), both BT-5s and BT-7s were used. Again the BT tank generally outclassed the lightweight enemy tanks. Against Finland during the Winter War, mainly BT-2 and BT-5 tanks were less successful. The Finnish forces were well-led, highly motivated and defended very constricted terrain. The thinly-armored BT tanks were very vulnerable to dug-in Finnish anti-tank guns (especially the 37mm Bofors, but also the 20mm Lahti) and routinely destroyed as long as there was a gun available in that sector.

During the Second World War, BT-5 and BT-7 tanks were used in the 1939 Soviet invasion of Poland, and in large numbers in the battles of 1941 - during which many were abandoned or destroyed. A few remained in use in 1942, but were rare after that time.

The Red Army planned to replace the BT tank series with the T-34 and had just begun doing so when the German invasion (Operation Barbarossa) took place.

In the Far East, a significant number of BT-7 tanks took part in the invasion of Japanese-occupied Manchuria, during August 1945. This was the last combat action of BT tanks.

Technical legacy
The BT tank series was numerous, forming the cavalry tank arm of the Red Army in the 1930s, and had much better mobility than other contemporary tank designs. For these reasons, there were many experiments and derivatives of the design, mostly conducted at the KhPZ factory in Kharkov, Soviet Ukraine.

The most important legacy of the BT tank was the T-34 medium tank, designed by the same bureau, and drawing many lessons from the fast tanks. Along the way, an important technical development was the BT-IS and BT-SW-2 testbed vehicles, concentrating on sloped armour. This proof-of-concept led directly to the armour layout of the T-34.

BT tank chassis were also used as the basis for engineering support vehicles and mobility testbeds. A bridgelayer variant had a T-38 turret and launched a bridge across small gaps. Standard tanks were fitted as fascine carriers. The RBT-5 hosted a pair of large artillery rocket launchers, one on each side of the turret. Several designs for extremely wide tracks, including, oddly, wooden 'snowshoes' were tried on BT tanks.

The KBT-7 was a thoroughly modern armoured command vehicle that was in the prototype stage when World War II broke out. The design was not pursued during the war.

In the Kiev maneuvers of 1936, foreign military observers were shown hundreds of BT tanks roll by a reviewing stand. In the audience were British Army representatives, who returned home to advocate for use of Christie suspension on British cruiser tanks. The British A-13, Crusader, and Cromwell tanks all used Christie suspension designs. Interestingly, the pointed shape of the hull front armor on the BT tank also influenced the design of the British Matilda tank.