The Historian Team.
The Sturmgeschütz III was the first in producing an assault gun that was build on a Panzer III chassis but were turret-less because the original Panzer III turret ring could not handle the kwk 37 turret housing. The StuG would be a main contributor of anti fortifications for Grenadier troops, and later on in 1942 as a tank destroyer.
This is when the StuG III Ausf. F upgrade happened when kwk 37's were replaced by kwk 40's to be a main anti tank, infantry support role in 1942 before Panzerschrecks in 1943. What made it different than a Panzer III or IV were that StuG's were part of the artillery divisions. What were unique about this tank destroyer were that it was not part of any Panzer divisions. That meant even infantry or Luftwaffe ground forces can use them. That also brings a point that the Sturmgeschütz series were the most produced armored vehicle made by the Germans.