BT Fast Tank

The BT series of tanks were a curious amalgam of American and Soviet technology. Although originally based on the imported Christie convertible tank, the Soviet versions quickly departed from the American originals, particularly in terms of armament. They were selected by the Red Army as the basis for their new mechanized forces, and were built in larger numbers than any tank of the 1930s except for their stable-mate, the Soviet T-26 infantry tank. The BT saw its combat debut in 1937 in the Spanish Civil War, and subsequently was used in combat against the Japanese Army along the Mongolian frontier in 1938–39, and again in the invasions of Poland and Finland in 1939–40. By the outbreak of war with Germany in 1941, the large Soviet tank park contained a motley selection of mechanically exhausted BT tanks from the early production runs, along with newer BT tanks from the later batches. Due more to poor training, poor tactics, and operational incompetence, the large fleet of BT tanks was largely destroyed in the great tank battles in the summer of 1941. Small numbers of BT tanks survived into the 1942 campaigns, and there was small-scale use in the Far East in 1945. Aside from being an important design in its own right, the BT series is perhaps best remembered as the forerunner of the legendary T-34 tank.

THE BT-5 TANK

By 1932, a variety of programs were underway at Firsov’s KB-T2K tank bureau to improve the basic BT-2 design. The BT-3 converted the design from imperial measurements to metric. The BT-4 project replaced the tank’s riveted construction with a fully welded hull. Over the years, purported photographs and drawings of a BT-4 with the twin turrets from the T-26 infantry tank have appeared in print and on the Internet; these are a hoax. In 1932, plans were underway for a follow-on to the BT-2 compatible with the new 45mm tank gun. At least three configurations were considered, the BT-5-M5 with the existing Liberty/M-5 engine, the BT-5-M-17 with the new M-17 gasoline engine, and the BT-5-BD-2 with the new BD-2 diesel engine. The latter two engine designs were not ready for serial production at the time so, as a result, the baseline BT-5 was fitted with the M-5 or reconditioned Liberty engines. The diesel-powered prototypes were sometimes designated as BT-5diz (diz = dizelniy, diesel).

The pilot for the BT-5 was completed on October 21, 1932 without the turret. The first batch of five new hulls and 25 turrets from the Mariupol plant arrived in Kharkov in November 1932 for assembly. The first fully equipped tank rolled out of the plant on January 1, 1933. The most obvious change between the BT-2 and BT-5 was the new turret with the 20K Model 1932 45mm tank gun. This 45mm tank gun was a derivative of the 19K 45mm towed antitank gun that was itself derived from the 37mm Rheinmetall gun. The caliber had been increased from 37mm to 45mm to permit the use of a larger and more powerful high explosive projectile; anti-armor performance was modestly improved as well. The new 45mm gun was one of the most effective tank guns of its day, offering both good anti-armor penetration and a good high explosive performance against unarmored targets. The early Model 1932 guns had a host of problems, so the design was upgraded as the Model 1934.

There were plans to design a common turret for both BT-5 and T-26 tanks and Kharkov’s Anatoliy Kolesnikov collaborated with colleagues from plant No. 174 in Leningrad, the main T-26 production facility. Due to manufacturing issues, two different turret configurations were initially manufactured. The Mariupol steel plant built 230 turrets with a small rectangular bustle attached to the rear of a riveted, cylindrical turret with a single large roof hatch. Although a few of these were mounted on the T-26 tank, most were used on the new BT-5, since Mariupol in Ukraine was closer to the Kharkov plant. The Izhorsk steel plant manufactured a more refined welded turret with the larger “integrated” bustle and twin roof hatches, and this “elliptical turret” (ellipticheskaya bashnya) became the standard type. Both turret types used the same gun mounting incorporating both the 45mm 20K gun and a coaxial 7.62mm DT machine gun.

The first batches of BT-5 tanks were sent to the Red Army’s premier tank unit, the newly expanded 5th Kalinovskiy Mechanized Corps. By 1933, the Red Army was well underway to adopting radios on its tanks, and an initial batch of 20 BT-5s with the 71-TK-1 Shakal (Jackal) radio transceiver were completed at the end of 1933, sometimes called BT-5RTs (radiyniy tank). These tanks were easily distinguishable from the standard “line tanks” (lineyniy tank) due to the use of an insulated clothes-line antenna around the turret. Eventually, some 325 BT-5RT tanks were completed of the 1,946 BT-5 tanks manufactured in 1933 and 1934, or about one in six tanks.

While production of the BT-5 was underway, work started on the BT-6 tank to extend its effective range. The pilot BT-6 tank was based on the earlier BT-4 with welded hull but it incorporated an additional large fuel tank at the rear of the hull. In the event, this project was short-lived and only a single test vehicle was completed.