15 cm sIG 33
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.
Additional Information: en.wikipedia.org/wiki/SIG_33