The BT series of Soviet "Fast Tanks" was born out of a John Walter Christie design in the early 1930s featuring an American suspension system and engine. The initial Soviet influences produced the 37mm-armed BT-2 out of the original Christie BT-1 with the BT-3 following based on metric measurements as opposed to Imperial. The BT-4 proved just three prototype examples with welded hulls and revised suspension systems. In 1933, the series received a more definitive existence with the unveiling of the BT-5 sporting a 45mm main gun and coaxial 7.62mm DT machine gun.



Even while the BT-2 was being worked on, the BT-5 was already being formed as early as 1932 and was intended as a modernization of the preceding type. The BT-5 retained the original's operating crew of three personnel made up of the driver in the front-center hull and the commander/gunner and ammunition handler in the turret. The internal layout was conventional with the driver in front, the fighting compartment at center and the powertrain at the rear. The turret was set well-forward of amidships which was a featured carried over into the upcoming war-winning T-34 Medium Tank. The running gear remained the same, dominated by four large pressed steel road wheels (now reinforced and no longer cast steel) to a hull side and a track link system encompassing the arrangement. Like the BT-2 before it, the BT-5 could see its tracks removed through a 30-minute manual process to which the vehicle could then run along its wheels, being steered by the front-most pair. This allowed for improved operational ranges across ideal, even surfaces (the tracks proved beneficial on uneven terrain).



Compared to the BT-2, the BT-5 was heavier (11.5 tons to 10.2 tons) while, dimensionally, its size was comparable. Armor protection remained 13mm at the thickest facing with 6mm along lighter, more vulnerable areas. The BT-5 was also powered by the American Liberty-based M-5 gasoline-fueled engine of 400 horsepower allowing for speeds of up to 45 miles per hour with a road range out to 200km. The design was decidedly slower than the BT-2 (45mph to 62mph) and limited in operational range (200km to 300km) on roads. External fuel stores could be fitted for increased ranges.



The major upgrade to the BT series came in the form of the larger-caliber 45mm Model 32 series main gun over that of the original's 37mm offering, this in a redesigned turret. 115 x 45mm projectiles were carried aboard. Defense was through a coaxial 7.62mm DT machine gun. Instead of the 13mm penetration value of the 37mm gun, BT-5 crews enjoyed penetration of up to 37mm of armor thickness at ranges reaching 1,000 meters. Ammunition options for the main gun included an armor-piercing (AP) and high-explosive (HE) type allowing the crew to engage both armored and unarmored targets with some level of success. The command vehicle version of the BT-5 retained its combat capabilities though the required additional communications equipment limited projectile stowage to 75 rounds.