In 1939, a team at the plants. Kirov in Leningrad, began work on a tank marked initially SP, and later object 126 or T-126 (SP). Structurally he alluded to the T-34, and was supposed to be the successor to the T-26. And the latter during the Winter War with Finland turned out to be already outdated design. It is a great loss suffered among the T-26 was the cause of the order of work on the T-50. The first prototypes of the tank was built in 1940. After preliminary studies, prototype submitted Factory in Leningrad, which was to take the series production tank. Following the design changes, created a new prototype called object-127 (T-127), which was then sent to manufacturing. From the initial design of the object 126, differed among others lower weight, which is mainly achieved by reducing the thickness of the shell from 45 to 37 mm. For a tank, a new diesel engine W-4 with 300 hp. After testing two new prototypes that were built in January 1941, Tank T-50 was adopted by the Red Army in April 1941. Factory no. 174 managed to produce only 50 units. Then the plants were evacuated to Nizhny Tagi?u and Omskaa. The plant in Omsk produced just 15 vehicles, and then began production of T-34 tanks. Overall, along with prototypes were built 65 cars T-50.