The Panzer I was the first tank produced in mass quantities by Germany. After its defeat in World War I, the development of tanks was banned in Germany. Following the A-type, which began production in 1934, an improved B-type was introduced in 1936. The 57-horsepower engine of the A-type was upgraded to 100 horsepower, and the welded chassis was extended by about 40 cm. The Panzer I was armed with two MG13 machine guns. Originally developed for training purposes, the Panzer I saw action during the Spanish Civil War, which broke out in 1936, during the invasion of Poland in September 1939, on the French front in 1940, during the invasion of the Balkans in 1941, and in other early stages of the war.