Development of the T-50 started as the SP project ("Soprovzhdeniya Pekhoty", 'Infantry Support') in 1939 at the OKMO design bureau in the S.M. Kirov Factory Number 185 in Leningrad, under the direction of, and headed by, L. Troyanov and I. Bushnevov, to create a light tank replacement for the T-26 and BT tanks. Initial prototypes, called T-126 and T-127, were not much improved over the T-46-5 project which had been abandoned earlier that year, but the heavier T-126 was selected for further development. The design bureau was gutted during the Great Purge, and was unable to continue the project, so it was transferred to the K.E. Voroshilov Factory Number 174 in Leningrad, May 1940, where two prototypes from the Voroshilovsky and Kirovsky factories were tested. The first 2 vehicles were finished at Factory No. 174 in Leningrad in late 1940. Troyanov completed the T-50 design in January 1941. After a few modifications it was ready for delivery in April 1941. Production was then authorized, but due to technical problems, it was unable to proceed. The chassis was supposed to be based on the T-40, however, the suspension operated differently.