The 15 cm sIG 33 (schweres Infanterie Geschütz 33) was the standard German heavy infantry gun used in the Second World War. It was the largest weapon ever classified as an infantry gun by any nation. Sources differ on the development history, but the gun itself was of conventional design. Early production models were horse-drawn, with wooden wheels. Later production models had pressed steel wheels, with solid rubber tires and air brakes for motor towing. The sIG 33 was rather heavy for its mission and it was redesigned in the late 1930s to incorporate light alloys in an effort to save weight. This saved about , but the outbreak of war forced the reversion back to the original design as the Luftwaffe had a higher priority for light alloys before more than a few hundred were made. A new carr