The Sturmpanzer (much better known by the name given to it by Allied intelligence, Brummbär) was an infantry assault gun built around the Panzer IV chassis. Its design was characterized by a box-like superstructure which housed a Skoda-designed 15-cm StuH43 gun which was intended for use for direct infantry fire support in urban areas. Given that it was expected to be used in close combat situations, it was heavily protected with up to 100 mm armor thickness at the front augmented by a modest slope and use of Zimmerit anti-magnetic paste. The front superstructure was interrupted only by the driver's station which protruted to the left of the gun, with a Tiger I driver's sight also installed. Firing ports were also provided for MP 40 machine guns with later series also adding a ball mount for an MG 34. The Brummbär was first deployed to the Battle of Kursk and saw action on the Eastern Front, Italy, and Northwest Europe with some notable actions including Anzio, the Battle of the Bulge, the Warsaw Uprising, and the defense of Budapest. Its relatively low production run (by wartime standards) meant it only equipped three Sturmpanzer-Abteilungs (batallions) plus one company.

Initial production of the Sturmpanzer began in April 1943 based on Panzer IV Ausf G chassis although a small number were Ausf E/F conversions. There were no variants aside from the basic version although improvements were made throughout the production run. The second series were based on the Ausf H, with additional armor to the driver compartment. The third series had minimal changes while the fourth series had a redesigned superstructure, commander's cupola, Ausf. J engine, and provision for a MG 34 machine gun.