Even before the Soviet light tank T-38 officially entered service, it became obvious the vehicle didn’t satisfy even half the requirements asked when it was first requested. In addition, the concept of an amphibious light tank with purely machine-gun armament, introduced by the British to the Soviets, turned out to be completely outdated by 1936.
Unfortunately, the Soviet tank industry could not offer anything better at the time. As an alternative, to the T-38 series, the T-43 series was proposed, as well as improved versions of the earlier T-37 series, but none of them fulfilled the requirements. In order to close this gap, the new chief of the ABTU, Bokis, ordered the creation of a completely new reconnaissance tank, designed to conduct long-range reconnaissance and long-range raids in groups”.
Technical requirements issued in the fall of 1937, stated the vehicle shouldn’t be amphibious, with a wheel-track type of the BT series and a mass not higher than 8 metric tons. The armament should include a 12.7mm DK machine gun, with 500 rounds, mounted in the turret and a 7.62mm DT machine gun in the hull with 2,500 rounds.
The tank received the designation of T-51 and was developed as part of the “Castle” project, where the Swedish Landsverk L-30 wheeled/tracked tank was taken as the basis. The choice in favour of the Scandinavian vehicle wasn’t accidental, the L-3 was well protected, its armament included a 37mm gun and two machine guns, and most importantly, the crew could change between tracks to wheels and back, without having to leave the vehicle.
However, by January 1938, the requirements from ABTU were significantly changed. The new requirements demanded the vehicle to be equipped with a 45mm or a 37mm gun. Ammunition was also changed respectively to 61 rounds and 1,3000 rounds. The crew was increased to three to include the loader.
These changes were quite reasonable, especially considering the experience gained while using light tanks in the Spanish civil war, showing that the concept used in the L-30 had been completely abandoned. According to the new project, the change would be carried out like in the BT series tank, with the removal of the tank tracks, allowing the tank to move with it’s road-wheels. It was also supposed to have a PT-1 and T-29 aircraft engine, with a 270 hp, giving it an estimated speed of 70 km/h. The armour would be more consistent with the T-26 series, with vertical armour plates ranging 13 to 15 mm thickness, while hull and turret roof would be 8 mm thick. According to the designers, the vehicle should be able to protect it’s crew against 12.7mm calibre guns, at a distance of up to 200 meters.
The tank received the name of Object 116 (T-116), but this change had no effect on its future fate. According to the ABTU estimates, it was impossible to create a light tank with the required performance and a mass of only 8 metric tons. This ultimately decided it’s fate, all work on the T-116 was cancelled and the project was scrapped at the beginning of 1938.