Tanks / USSR
BT-7 fast tank
When the Red Army tank staff decided to modernize its tank fleet during the late 1920s it authorized the design bureaux to use whatever sources they liked to obtain the best ideas available. Accordingly many promising design concepts from all over the world were embraced, and among these were ideas of the American J, Walter Christie, His advanced suspension designs had little effect in his own country at that time, but the Soviets embraced his concepts willingly and took them over for their own further development. The Christie suspension was integrated into the BT series (bystrochodya tank, or fast tank).

The first Soviet BTs were copied exactly from a Christie prototype delivered to the Soviet union in 1930 and designated BT-1. The first Soviet model was the BT-2, and from 1931 onwards the BT series progressed through a series of design developments and improvements until the BT7 was produced in 1935. Like the earlier BT tanks the BT-7 was a fast and agile vehicle intended for Red Army cavalry units, and was powered by a converted aircraft engine. The suspension used the Christie torsion bars that allowed a large degree of flexibility at high speeds. The hull was allwelded and well shaped, but the main gun was only a 45-mm (1.77-in) weapon, although this was still larger than that fitted on many contemporary equivalents. The secondary armament was two 7,62-mm (0,3-in) machineguns, and armour varied from 10 to 22mm (0,39 to 0.87 in). The BT-7 was intraduced in to service m 1935 and was produced in two main versions, both armed with a 45mm (1.77-in) gun. Although fast and handy in action, the BT-7 proved to be too lightly armoured, but it led in time to the development of the T-34.

The BT-7 proved to be very popular with its users. By the tme it entered service (in its original BT-7-1 form with a cylindrical turret, replaced by a conical turret in the BT-7-2) many of the automotive snags that had troubled some of the earlier BTs had been eliminated, and the BT-7 thus proved to be fairly reliable. Also, by the time it appeared there were many variants of the BTs: some were produced as flamethrower tanks, and there was a special BT-7A close-support version carrying a short 76.2-mm (3-in) main gun. Other expérimentais included amphibious and bridging tanks, and variants with various tracks to improve terrain-crossing capabilities.

The BT-7 did have one major tactical disadvantage in that it was only lightly armoured. On the entire BT series armour protection had been sacrificed for speed and mobility, and once in action during 1939 the BTs, including the BT-7, proved to be surprisingly vulnerable to anti-tank weapons as small as anti-tank rifles, BT-5s had demonstrated this fact when small numbers were used during the Spanish Civil War, but even though the BT-7 had some armour increases this was still not enough, as revealed in Finland during 1939 and 1940. As a result the design of a successor to the BT series was undertaken and this led ultimately to the adoption of the T-34, Variants of the BT-7 were the BT-7-l(U) command tank and BT-7M (or BT-8) improved model with full-width and well-sloped glacis plate plus a V-2 diesel engine. Thus the BT-7 played its major part in World War II well before the Germans invaded the Soviet Union in 1941. Large numbers were still in service in 1941, but they fared badly against the advancing Panzers. Despite their mobility the Soviet tank formations were poorly handled and many tanks, including BT-7s, were lost simply because they broke down as the result of poor maintenance or poor training of their crews. It was an inauspicious beginning for the Red Army, but worse was soon to follow and the large fleet of BT-7s was virtually eliminated by the end of 1941.

The BT-2 was the first Soviet tank design to incorporate the Christie suspension, and led to a whole string ofBT variants that were eventually developed into the T-34 series. The Christie suspension gave the BT-2 a good cross-country performance, as this photograph graphically demonstrates.
 
Specification BT-7 Crew: 3 Weight: 14 tonnes Powerplant: one M-17T V-12 petrol engine developing 373 kW (500 hp) Dimensions: length 5.66 m (18 ft 6.8 in); width 2,29 m (7 ft 6 in); height 2.42 m (7 ft 11.3 in) Performance: maximum road speed 86 km/h (53.4 mph); maximum road range 250 km (155 miles); fording 1.22 m (4 ft); gradient 32∞; vertical obstacle 0.76 m (2 ft 6 in); trench 1.83 m (6ft)
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