Despite the development of the formidable T-34, the idea of a
new mass-produced tank emerged inside the Soviet military
circles. So two Soviet factories in Leningrad (Kirovsky factory
and Voroshilovsky factory No.174) were ordered to develop a new
14-ton tank armed with 45 mm gun and protected by medium armor,
similar to T-34. In 1939, the Kirovsky factory was ordered to
develop a light CS tank (close support tank). In 1940 the first
prototype, named "Object 126" or T-126SP, was developed,
manufactured and tested. Its protection was equal to the T-34's:
its welded hull was assembled from 37 mm homogeneous armor
plates; its roof was composed of 20 mm plates. Frontal, upper
side and rear armor plates were sloped 40-57 degrees. The new
tank did have the 45mm Tank Gun Model 1932/38 supplied with 150
rounds plus a coaxial 7.62 mm DT machine-gun. Additionally, it
was armed with the 7.62 mm DS bow machine-gun. The tank was
powered by a 250 hp V-4 diesel engine, which provided the 17-ton
vehicle with a maximum speed