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 (Christie Tank). 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.
Christie had tried unsuccessfully 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 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. The original Christie tanks were designated fast tanks by the Soviets, abbreviated BT (later referred to as BT-1). Based both on them and on 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 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. After two new variants (BT-3 and BT-4) the BT-5 will have a new designed and bigger cylindrical turret with an stronger 45mm M1934 gun. Later some modifications on the BRT-5 will lead to the BT-7. This light tank with his small 47mm gun is no match against the heavy tanks. However, his speed and small size can make it a hard target to destroy. The movie left show us how fast the tank was in real life. The Christie's tanks are one of the best tank designs ever! Because since the debut of the Christie's, the design had later be using in new tank designs! In FHSW a lot of tanks use the Christie suspension. Those are the : Russian T-34 serie, T-29 serie and the SU variants, British Crusaders, Cromwells and then Sp 6 Pdr Molins and the Polish 14TP. Despite the large wheel size, the LT vz 38 did not use a Christie suspension! Until now, the Christie suspension design is still be use in modern tanks. The Italians also used the BT-7 (not in FHSW) and use the tank as self-propelled howitzer wich becomes the BT-42.