The Sturmpanzer IV (also known as Sturmpanzer 43 or Sd.Kfz. 166) was an armoured infantry support gun based on the Panzer IV chassis used in the Second World War. It was known by the nickname Brummbär ("grizzly bear") by Allied intelligence, a name which was not used by the Germans. German soldiers nicknamed it the "Stupa", possibly a contraction of the term Sturmpanzer.
The result was the Sturmpanzer IV, which used a Panzer IV chassis with a new, fixed superstructure housing the 150 mm Sturmhaubitze (StuH) 43 L/12 gun. This fired both high explosive and shaped charge anti-tank rounds. Thirty eight rounds, with separate propellent cartridges, could be carried.
The original design of the Sturmpanzer IV suffered from a series of flaws, which were gradually solved during the production process. The most important flaw was the high weight and recoil of the StuH 43 gun, which overloaded the Panzer IV chassis and made the entire vehicle top-heavy. Furthermore, early vehicles suffered from transmission failures and were underpowered.
Another significant flaw was the absence of a machine gun which made it easy for enemy infantry to attack the vehicle at close range. Early vehicles carried a MP 40 sub-machine gun inside, which could be fired through firing ports in the side of the superstructure.
In October 1943 it was decided that the Sturmpanzer IV's superstructure as well as the StuH 43 gun needed to be redesigned to fix these flaws. A new and lighter version of the StuH 43 gun was produced, the StuH 43/1 L/12. This gun was used from the second production series onwards.
A new superstructure was added in mid-1944 which featured a redesigned gun collar, as well as a general reduction in height of the superstructure. This redesign also introduced a ball mount in the front superstructure for a MG34 machine gun with 600 rounds.
After some teething trouble with early production models, the Sturmpanzer IV proved itself to be an excellent fire support vehicle.