The Sturmpanzer (also known as Sturmpanzer 43 or Sd.Kfz. 166) was a German armoured infantry support gun based on the Panzer IV chassis used in the Second World War. It was used at the Battles of Kursk, Anzio, Normandy, and was deployed in the Warsaw Uprising. It was known by the nickname Brummbar (German: "Grouch") by Allied intelligence, a name which was not used by the Germans. German soldiers nicknamed it the "Stupa", a contraction of the term Sturmpanzer. Just over 300 vehicles were built and they were assigned to four independent battalions.
The Sturmpanzer was a development of the Panzer IV tank designed to provide a vehicle offering direct infantry fire support, especially in urban areas. It used a Panzer IV chassis with the upper hull and turret replaced by a new casemate-style armoured superstructure housing a new gun, the 15-centimetre Sturmhaubitze (StuH) 43 L/12 developed by Skoda. It fired the same shells as the 15 cm sIG 33 heavy infantry gun. Thirty-eight rounds, with separate propellant cartridges, could be carried. It used the Sfl.Zf. 1a sight. The combined weight of the shell and cartridge (38 kilograms for an HE shell and 8 kilograms for a propellant cartridge) made the work of the loader arduous, especially if the gun was elevated to a high angle. An MG 34 machine gun was carried that could be fastened to the open gunner's hatch, much like the arrangement on the Sturmgeschütz III Ausf. G. Early vehicles carried an MP 40 sub-machine gun inside, which could be fired through firing ports in the side of the superstructure.
The driver's station projected forward from the casemate's sloped frontal armour plate and used the Tiger I's Fahrersehklappe 80 driver's sight. The fighting compartment was, albeit poorly, ventilated by natural convection, exiting out the rear of the superstructure through two armoured covers. Sideskirts were fitted on all vehicles. Early vehicles were too heavy for the chassis, which led to frequent breakdowns of the suspension and transmission. Efforts were made to ameliorate this from the second series onwards, with some success. In October 1943, it was decided that the StuH 43 gun needed to be redesigned to reduce its weight. A new version, some 800 kilograms lighter than the StuH 43, was built as the StuH 43/1. Some of the weight was saved by reducing the armour on the gun mount itself. This gun was used from the third production series onwards. Zimmerit coating was applied to all vehicles until September 1944