Like the similar Soviet T-26, the 7TP was a development of the British Vickers 6-ton (Mk.E) which the Poles purchased and licensed for local production. The main new features of 7TP were: a better, more reliable and powerful diesel engine (which made the 7TP world's first diesel tank), 37 mm anti-tank gun, and slightly thicker armor (17 mm in front instead of 13 mm). Only about 132 tanks were produced between 1935 and the outbreak of the war. The weight increased after the initial 7-tonne prototype was made and the actual serial tanks weighed 9.9 tonnes.