At the time of the Sudeten Crisis the vast majority of tanks in German service, more than 1,000, were the lightly armed PzKpfw I. The vehicle was originally designed as a training tank with extremely light armor of between 7mm and 13 mm thickness, and only two 7.92mm Maschinengewehr 13 machine guns as armament. The PzKpfw I entered Wehrmacht service in 1934 and took part in all major campaigns through the invasion of the Soviet Union in 1941. The four-cylinder Krupp M 305 air-cooled engine moved the 5.4 ton tank to a maximum speed of 23 miles an hour. The PzKpfw I had a two-man crew.