It was an interim design until Jagdpanzer IV could begin production. Also the Alkett factory's production had been disrupted by bombing so Krupp was asked in December 1943 to produce the StuG IV. Driver's section was modified to have an access hatch and 2 periscopes in an armored cab.
On December 6, 1943, Hitler ordered the StuG III superstructure fitted to the PzKpfw IV chassis. Built on PzKpfw IV Ausf G and PzKpfw IV Ausf H chassis.
Some models had 6" of concrete added to the superstructure front. The cast Saukopfblende mantlet was introduced in February 1944.
A Nähverteidigungsgerät (close defense weapon) was also installed.
In the summer of 1944 the external machine gun was replaced by a remote controlled machine gun.