The German sIG 33 heavy infantry gun was mounted on a number of vehicles to produce a self-propelled gun. The first appeared in 1940, and improved versions were still in production in 1944.
The early vehicles used ordinary sIG 33s, but an sIG 33/1 was developed for use on later vehicles. The 15 cm Sturmhaubitze 43 gun used on the Sturmpanzer IV was an entirely new design developed by Skoda that used the same ammunition as the sIG 33.