The interbellum period was a time when armoured forces were actively pondering the meaning of their existence. Many types of tank were invented by 1920, among which was the support tank. This tank was created because 37-57 mm guns on vehicles of the time were useful for fighting infantry and sometimes enemy tanks, but were insufficient against even light fortifications.
All tank-building nations developed this kind of tank. The British installed a 94 mm howitzer on the Medium Tank MkI. The Germans picked a 75 mm short-barrelled gun for the experimental Grosstraktor, assuming that it will be enough to complete its tasks. The Soviet Union did not remain an observer either.
BT-7 Artillery, not to be confused with BT-7A
Two prototypes among Soviet tanks of the early 1930s require a closer look. One was a project by a self-taught engineer Nikolai Dyrenkov, built in metal. This was a BT-2 with a new turret and a 76 mm gun. The vehicle underwent testing, but it was discovered that the turret was too small for the crew to work in it. The project was shut down. Experiments with 76 mm guns continued on the chassis of the T-26 light tank, and they got quite far. A second prototype appeared, the T-26-4. After that, the BT was abandoned as a platform for a 76 mm gun, but not for long.
In 1934, the Kharkov Locomotive Factory began work on the BT-7 tank. At first, designers proposed that it should be armed with a 76 mm gun in a new turret. However, the prototype turned out to be as cramped as Dyrenkov's design. The BT-7 entered production with the same turret as its predecessor and the same 45 mm gun.
The idea to put a more powerful gun into the BT-7 remained, especially since the T-26-4 project was promising, and even made it to a trial production batch of 5 tanks.
The designers had a logical idea: combine the hull of one tank and the turret of another. HPZ already had experience with the T-26, since the BT-7 with a large caliber gun was developed on the basis of the T-26 artillery tank project. In April of 1935, one turret was sent to Kharkov. The design was changed a little and installed on the BT-7 hull. In October of 1935, the prototype was sent to trials. Modern sources refer to this tank as the BT-7A, but this is incorrect. That index was used to refer to early BT-7 vehicles. The vehicle with a 76 mm gun was called "BT-7 Artillery".
Trials went successfully, but the fate of the tank hung by a thread. This happened due to an accident on September 19th, 1935 with one of the T-26-4 vehicles, where gunpowder gases ruptured the gun breech during trials. Even though the KT-28 was a temporary gun choice and would have been replaced with a more modern gun, this incident caused the termination of the T-26-4 project.
The "lucky seven" was more fortunate. Work never ceased, and the tank eventually made it to mass production.
Brief Life at Peace and War
The first batch of BT-7 Artillery tanks was assembled in late August of 1937. In January of 1938, there were over 150 of them, not that many, but a shortage of KT-28 guns caused production to stop. The cause was pretty common for the time: the gun was removed from production, and no adequate replacement was found. This was the end of the first Soviet artillery tank. 132 vehicles were used by the army, supplementing regular BT-7s. One other vehicle was used as a mount for experimental weapons.
The last burst of activity around the BT-7 Artillery happened in 1940, when Vasiliy Grabin's F-32 gun entered production. It was meant for the perspective KV and A-34 (future T-34) tanks. The military decided that there should be no reason for this new weapon to skirt existing designs. It was planned that the BT-7 Artillery would receive new guns in 1941, if not with first priority. The start of the war interfered with these plans.
On June 1st, 1941, 122 vehicles of this type were in military service, most of them in the Kiev Military District. Due to their small numbers, BT-7 Artillery tanks left nothing behind but photos of wrecks and records of written off vehicles. The last of these tanks fought in the Battle of Moscow in November of 1941. The 58th Tank Division arrived from the Far East with these types of tanks. It lost almost all of them in only a few days of fighting at Volokolamsk.
Despite its difficult history, the BT-7 Artillery was an important step in Soviet tank building. It was the first mass production vehicle that could be put in the SPG class. The KV-2 was built in 1940 according to a similar principle. As with the BT-7 Artillery, its job was to aid its forces in breaking through enemy fortifications.
Original article available here.