Initially the vehicles were formed into independent assault gun battalions which had three companies of ten tanks each, and a commander with his own. Ten of these battalions were deployed in June 1941, for Operation Barbarossa. By July 1942, there were 19 such battalions, and by the end of 1943, there were 37.
Starting in late 1943, the German High Command started assigning assault guns to the tank destroyer company, which was part of the anti-tank battalion in the 1944 pattern infantry divisions.
The 42 assault gun battalions in service in the summer of 1944 were designated to be brigades. In late 1944 a grenadier platoon was to be added to provide support. By January 1, 1945, there were 39 assault gun brigades, and only 7 of these had the grenadier platoon.
Some StuGs were being assigned to panzer divisions in 1944 to offset the shortages of regular tanks.
Grossdeutschland and some Waffen-SS units had assault gun units as part of the division.
The 341st and 349th assault gun brigades fought in the Normandy Campaign in 1944. The 2nd, 9th, and 10th SS Panzer Divisions had 2 companies each of StuG IIIs in Normandy. The 1st and 2nd SS Panzer Division each had tank destroyer battalions supplied with StuG IIIs as the Jagdpanzer IVs hadn't reach the units yet.
Battle of the Bulge
Many units participating in the offensive through the Ardennes had StuG IIIs. One unit, the 244th Assault Gun Brigade, destroyed 54 American tanks for a loss of two of its own.
190th Assault Gun Brigade
In West Prussia, during the defensive fighting in the spring of 1945, it distinguished itself enough to be mentioned in German High Command communiques twice. On February 26, 1945, the brigade destroyed 104 enemy tanks, for a loss of 4 assault guns. On March 3, 1945, the brigade destroyed its 1,000 tank since being formed in 1940. Because of its success it was evacuated from West Prussia to be used in the defense of Berlin.
232nd Assault Gun Brigade
It was cut off in the Samland peninsula in East Prussia in the spring of 1945. It combined itself with other brigades to form the largest assault gun formation of the Germany Army, with 2,000 men and 47 assault guns in February 1945. However, by April 1945, it had lost its last assault gun. The remaining personnel were evacuated on May 8, 1945, to Hela from Danzig by barges. That night they were crowded onto a torpedo boat and made their way to Denmark.
243rd Assault Artillery Brigade
After being used as infantry on the Teltow Canal during April 1945, the unit received 40 brand new StuGs straight from the Alkett factory in Berlin. On April 14-15 they went into combat against the American bridgehead at Schoenenbeck on the Elbe River. They were then joined with the Theodor Korner Division in trying to relieve Berlin. They recaptured Treuenbrietzen, with support from Assault Gun Demonstration Brigade Schill, which was raised from the training school at Burg.
249th Assault Gun Brigade
On April 24, they collected 31 brand new assault guns from the Alkett factory in Spandau. On the 27th, German High Command ordered the unit to break through the recently closed encirclement of Berlin by the Soviets. The 249th broke through and setup positions at Friedrichshain, which was in the Berlin perimeter. The Knight's Cross was awarded to the brigade's commander. By the 30th, they only had nine assault guns left and were conducting a fighting withdrawal to Alexanderplatz. Its final position was at the Berlin Technical High School. After hearing of Hitler's suicide, the remnants tried to break out with its last three assault guns. These were destroyed near Spandau, but some of the crews and the commander were able to reach the Elbe and surrender to the Americans.
Some were supplied to Finland, Romania, Hungary, and Bulgaria.