For its time, the tank was well armoured and armed, but completely ordinary. In 1933, the chief of the Directorate of Mechanization and Motorization of the Red Army, I.A. Khalepskiy, ordered his engineers to turn this rank and file tank into an all-destroying armoured weapon. The goal was to "create a tank that carries 250 kg torpedoes, capable of destroying targets in the enemy rear."
150 kg from the sky
Tank torpedoes designed for the BT consisted of an aerodynamic hull with four stabilizing fins, filled with 130 kg of TNT. A light tank with a few of these rounds obtained colossal firepower. 250-TT torpedoes were primarily meant for destroying enemy fortifications, pillboxes, railroad structures, etc. Additionally, the BT could destroy enemy vehicles.
Engineers immediately raised several issues. For instance, if you mount a 400 kg weight on each side of the turret of a BT-5, can it still rotate? Will the launchers be sturdy enough? Finally, what will be the range or precision of the rocket? None of these questions could be answered with theoretical calculations, trials were necessary.
To start, engineers tested the hulls of the torpedoes in 1934-1935. 95 gunpowder charges were placed in the chamber and ignited. The hull held. It was time to try shooting from a mount. These trials were carried out at a proving grounds at Norislk.
The trials were carried out with six torpedoes, two were inert and filled with wet sand instead of explosives, the other four contained TNT. Trials showed that "the flight of all six bombs was correct and stable, the range when launched at an angle of 50 degrees is 1400-1500 meters." The four craters from the exploding torpedoes were measured to determine their power. The craters were 10 meters across and 4 meters deep on average.
Not good enough
It was time to shoot from the tank. On July 19th, 1936, a BT-5 with rockets mounted on the side arrived at the proving grounds at Podsolnechnaya station. The radiators on the rear of the tank were protected with special covers so they were not damaged by the exhaust.
The elevation was set manually, with a variation of 10 degrees. The first shot was fired with closed hatches, the second with opened hatches, to test the effect of the rocket exhaust on the crew.
The torpedoes flew correctly and were stable, with a difference in range of 100 meters, depending on the angle of elevation. The exhaust was deflected from the tank with no damage. The BT-5 turret could spin freely even with the torpedoes mounted. However, all was not as good as it seemed.
In order to zero in the torpedoes and create ballistics tables, many test shots were needed. Reloading the launchers was a risky task for the crew, who would have to exit the tank in the middle of the battle. A munitions carrier was supposed to partially resolve this problem.
Trials continued until November of 1936. Based on these trials, the commission composed a final list of drawbacks of the torpedo tank. The drawbacks were as follows:
- Large and bulky launcher.
- Decrease of the tank's combat performance.
- Small amount of torpedoes carried on board.
- Impossible to reload without leaving the tank.
- Torpedoes are not protected from machinegun fire.
- The projectile's range is short.
- The initial velocity is low.