The Sturmgeschutz III (StuG III) was an assault gun produced by Germany during World War II. It was the most-produced fully tracked armoured fighting vehicle, and second-most produced German armored combat vehicle of any type after the Sd.Kfz. 251 half-track. It was built on a slightly modified Panzer III chassis, replacing the turret with an armored, fixed superstructure mounting a more powerful gun. Initially intended as a mobile assault gun for direct-fire support for infantry, the StuG III was continually modified, and much like the later Jagdpanzer vehicles, was employed as a tank destroyer.
Learn more on Wikipedia