The T-50 was a light tank developed on the eve of World War II for the Red Army. The experience of the Spanish Civil War led to an effort to upgrade or replace the large Soviet tank fleet. Prior to 1939, most tanks in Red Army service were improved versions of foreign designs. For example, the most numerous tank, the T-26 light infantry tank, was a copy of the British Vickers 6-Ton tank with a Soviet-designed turret and 45 mm gun. However, just prior to and during the war, the USSR developed new light, medium and heavy tanks of wholly indigenous design. The T-50 light tank was intended to replace the T-26 infantry tank; in prewar planning, the T-50 was intended to become the most numerous Soviet tank, operating alongside the BT fast tank.