In the latter portion of the 1920s, the Soviet Army began looking to modernize their fleet of aging tanks. As such, it held a relatively open competition for its design bureaus to find the right mix of armament, speed and armor protection utilizing the best facets of existing tanks from all over the world. One of the designs of note became the M1931 light tank designed by American J. Walter Christie (1865-1944), a race car mechanic, inventor and mechanical engineer by trade. The M1931 utilized his globally-recognized "Christie" suspension system which used torsion bars that provided for a high degree of flexibility at above average speeds. As such, it played well in the creation of a "light" - or "fast" - tank system. While the development of his Christie suspension system was often overlooked in the United States, it found fame elsewhere in the world as the British, French and Russians all took note. Christie attempted to sell the US Army on his M1931 "Christie Tank" without success.
Between 1930 and 1931, Russia received delivery of two prototype examples (sans turrets and armament) of the Christie M1931 for evaluation (these sent under falsified papers claiming them to be farming tractors and not combat tanks). Utilizing an existing design for the Russians held some merit for they proved a more cost-effective engineering endeavor in the long run. After trials, the Russians liked what they saw in the Christie and reengineered the type for their own ranks as the BT ("Bystrochodnij Tankov" or "Fast Tank") light tank. A license to mass produce the Christie design was subsequently obtained by the government. The original production versions - the BT-1 and BT-2 were essentially direct copies of the Christie design and, of these two, only the BT-2 was the version that first featured Soviet-inspired modifications. The series ultimately evolved to include subtle variations to help simplify production and were powered by an engine originally utilized in aircraft. The BT-2 prototype was finished in October of 1931 and production began the following year. Primary armament centered around a 37mm main gun but ordnance shortages ensured that some were machine gun-only tanks. The subsequent BT-5 model was then up-gunned to a 45mm main gun armament. At any rate, this mating produced a fast and agile tank, giving birth to the definitive BT-7 model of 1935 with its new turret, new transmission, stronger armor and more powerful engine. Operational service for the BT-7 began in 1937 under the formal designation of BT-7-1 - these were identified by their cylindrical turret designs that were only later upgraded to a more conical shape.
Taken as a whole, the BT-7 design exhibited excellent cross country mobility thanks to her Christie suspension system and displayed equally excellent speeds on roads. The suspension was linked to eight large road wheels - four positioned to a track side - and each were independently mounted. To exploit the BT-7's adaptability for off-road actions, tracks of differing width could be adapted offering varying degrees of traction against varying terrain types as needed. The design of the BT-7 was such that the tracks could be completely removed within 30 minutes by the crew to allow for on road driving of the tank on its own wheels, the "drive" now being relocated to the rear sprockets and rear wheels while the front road wheels were used for steering. This feature, however, proved a novelty and was hardly ever used in practice, ultimately dropped from later BT production models. The idea behind this drive mode was to supply the tank with excellent wheeled road speeds in getting from point A to point B but this was really only effective on road driving. In a country where paved roads were limited in number, it made little sense in keeping the feature on future production forms. Furthermore, the track removal process was noted as laborious and complex for practical use.
Despite her light armoring throughout, the BT-7 was well-armed for the time in fielding a 45mm main gun in a rounded traversing turret, putting her on par with many of her contemporaries elsewhere. The main armament was further backed by a 7.62mm general purpose anti-personnel machine gun in the turret as a co-axially mounted weapon. Generally, 172 to 188 x 45mm projectiles were carried within the tank along with 2,394 rounds of 7.62mm ammunition. Some BT-7 models also fitted an additional 7.62mm machine gun, this in a rear-facing, trainable ball-mount along the back facing of the turret to protect the tank's rear against direct infantry attacks. Within time, it was found that this fitting was somewhat useless when pairing the tank with infantry squads. Infantry squads could now protect the BT-7 from direct, close-range enemy attacks.
Early production forms of the BT-7 sported riveted turret designs which brought about another level of danger to the crew. If suffering a direct hit from an enemy shell, the rivets holding the turret armor of the BT-7 in place presented bullet-like projectiles within the turret itself, able to cause severe damage to the crew, ammunition and critical systems alike. As such, production inevitably moved to a welded turret system. Once in practice, the BT-7 proved a reliable and sound mechanical implement of war, respected by her crews for her performance and ease of maintenance if properly maintained.
Externally, the BT-7 retained much of her original Christie appearance. She sported a highly identifiable sloping glacis plate straddled on either side by the track mud guards. The sides of the hull superstructure were equally well-sloped and helped to an extent in delivering awkward angles against incoming enemy projectiles. The hull was of all-welded construction. The driver sat at the forward center of the hull with an entry/exit hatch showcasing a simple forward vision slit. Directly to driver's rear was the traversing turret holding the main gun. The BT-7 was operated by a crew of three including the driver in the hull and two personnel situated in the turret to man the armament.
The BT-7 weighed in at just 13.5 tons and was powered by a single M-17 V12 diesel engine of 450 horsepower. This allowed for speeds in excess of 32 miles per hour with a range out to 217 miles. Armor was 6- to 22-mm thick across all facings providing for modest protection at the expense of speed. The BT-7 had a length of 18 feet, 7 inches with a height of 7 feet, 11 inches.
The chassis of the BT-7 served well to produce offshoot designs such as the close-support BT-7A artillery tank mounting the short-barreled 76.2mm cannon. The 76.2mm cannon was quickly found to be the cannon of choice when contending with the thicker German tank offerings and became standard armament of the upcoming - and highly successful - T-34 series of medium tanks. Beyond this variant, the BT-7 was also developed into a command tank under the designation of BT-7-I(U) with its increased communications equipment at the expense of additional ammunition. Offensives relied on such vehicles to promote clear communications and leadership between tanks in the field. The BT-7M (or BT-8) was later produced as an improved BT-7 form with a 500 horsepower V2 twelve cylinder diesel engine in a revised hull for improved survivability. Along with its 76.2mm main gun armament, the BT-7M also fitted a pair of 7.62mm machine guns for self-defense - one mounted in the turret and the other in the hull. Experimental versions went on to include bridging and amphibious models that never went to production.
As the previous BT-5s proved viable in the Spanish Civil War, it was only logical to expect success with the BT-7 when they were used en mass in the Soviet invasion of Poland. The tank became the primary armored vehicle to spearhead the Red Army in the operation. Poland was inevitably conquered by a combined force of Germans in the West and Soviets in the East with little help from the Allies.
However, the future of the BT-7 was put in doubt in subsequent actions in the Winter War with Finland and in the German invasion of the Soviet Union. Anti-tank weapons fielded by the Finns led to many a loss for the BT-7 ranks. By the time of the German invasion (under "Operation Barbarossa") in 1941, the BT-7 was in full operational service, available in some number, but essentially already having peaked in terms of effectiveness. Despite her having "modernized" Soviet tank forces some years before, the type was quickly shown to have major deficiencies, particularly in armor protection, when combating the new breed of German tanks. As can be expected, losses for the under-gunned and lightly armored system quickly mounted. Couple these inherent limitations with poorly trained commanders and crew and ill-maintained vehicles and one develops a recipe for battlefield disaster. After all, the BT-7 was, at its core, a light tank design and never truly meant to tangle with medium or heavy tanks by any regard. If anything, a light tank design was counted upon to provide armored reconnaissance or infantry support in carefully planned outings. As a direct assault implement, however, the BT-7 was obviously lacking in the key areas of protection and offensive output. By the end of 1941, large collections of BT-7 were either knocked out of action by the enemy or placed out of service through logistics. Any examples captured by the German army were reconstituted only for security duty to cover the rear from Soviet flanking maneuvers and not as frontline tools.
At any rate, the surprised Russians utilized whatever was in their stocks at the time to ultimately stave off extinction at the hands of the Germans. The German assault was eventually slowed down and halted, only to be repelled by a determined and, sometimes suicidal, Soviet resistance. Despite her obsolescence by the summer of 1941, the BT-7 no doubt played a role in the recovery of the Soviet Union and lent its successes into the design of the war winning T-34 medium tank still to come. In 1937, a new collection of Soviet talent was brought together to find the planned successor for the BT series. The group delivered the what ultimately became the T-34 itself.
With the BT-7's role all but completed in the West, Soviet authorities rerouted the tank for use in the August 1945 Soviet invasion of Manchuria in operations against the Japanese Army along the Russian border. The Soviet Army was put into action once more, just three months removed from the end of the European War, after an agreement was reached with Allied forces at the Tehran Conference in November of 1943. In these actions, the BT-7 proved far superior to all the armored infantry vehicles the Japanese could field. This would be the last recorded combat actions for all BT tanks, her legacy already having been secured in history. The Soviet invasion of Manchuria marked the largest operation in the 1945 Soviet-Japanese War with the end result being the liberation of Manchukuo (Manchuria) by the Russians. The resounding Soviet victory here played a role in the final surrender of the Empire of Japan to end World War 2.
Close to 5,000 examples of the BT-7 were ultimately produced, making up a large portion of the near 8,500-strong BT series family as a whole.