The 15 cm schweres Infanterie Geschütz 33was the standard German heavy infantry gun used in the war. It could fire 2 to 3 rounds per minute with an effective range of over 5000 yards. The sIG 33 could fire conventional ammunition (HE, Smoke & Hollow Charge) as well as a special Stielgranate 42. This round had a range of approximately 1100 yards. Unlike other Stielgranaten this version was not intended for anti-tank use, but rather for the demolition of strongpoints and clearing barbed-wire obstacles and minefields by blast effect.
The invasion of Ploand in 1939 had demonstrated that the (sIG 33) assigned to the motorized infantry regiments had a hard time keeping up with the armored units in combat.
The solution was to take a spare tank hull and mount the gun on it and provide some armor protection for the crew.
15 cm sIG 33 auf Fahrgestell Panzerkampfwagen I Ausf B (Sf)
Initially a Panzer I, ausf B was used. This was designated as the 15 cm sIG33 auf Fahrgestell Panzerkampfwagen I Ausf B (Sf) (aka Sturmpanzer I Bison). 13 mm armor plates provided protection for the crew in the form of an open topped, three sided box open at the rear. In truth this only protected the gunner and the gun from shell fragments and small arms fire; the loaders were completely exposed. The plates were tall enough to accomodate the gun which gave the vehicle a height of over 9feet. This made the vehicle difficult to hide. The gun was affixed to the tank chassis completely intact (wheels, carriage and all). This caused the fighting area to be so cramped that there was no room to store ammunition on board (it had to be carried seperately). The weight of the gun and armor overloaded the chassis and breakdowns were frequent.
Production & Deployment 38 were produced by Alkett in February 1940. 36 of these were organized into independent companies of six guns each.
schwere Infanteriegeschütz-Kompanie; mot.S 701-706 were assigned to the 1st, 2nd, 5th, 7th, 9th, and 10th Panzer divisions for the Battle of France and Operation Barbarossa. The 705th and 706th were destroyed during Barbarossa. Of the remaining companies only the 701st participated in the opening stages of the German summer offensive in Southern Russia in 1942, although it, and its parent 9th Panzer were transferred to Army Group Center by the end of the summer of 1942. The last reference to them is with the 704th Company of the 5th Panzer division during the middle of 1943.
15 cm sIG 33 auf Fahrgestell Panzerkampfwagen II (Sf)
The same sIG 33 gun was mated to a Panzerkampfwagen II chassis in an attempt to reduce the overall height of the vehicle and reduce the overloading caused by using the Panzerkampfwager I ausf B chassis.
In order to make this work correctly the Panzer II chassis had to be widened by 13 inches and widened by 24 inches (including adding a sixth roadwheel). 15 mm armor plates formed the sides and front of the open topped fighting compartment. The result was a vehicle that topped out at just over six feet, could carry 30 rounds of ammunition and was less prone to breakdowns. The downside of the lower profile was the crew was more exposed to shell fragements and small arms fire.
Production & Deployment Twelve were built by the end of 1941 and shipped to North Africa in early 1942. Two companies of six guns each were formed into the schwere Infanteriegeschütz-Kompanie (mot.S.) 707 and 708. The 707 was assigned to Schützen-Regiment 155 and the 708 to Schützen-Regiment 200 (both part of the 90th leichte Division). Both companies fought until the Axis surrender in Tunisia in May, 1943.
The deficiencies with the sIG 33 I and II led to the SIG 33B. An improved version of the sIG 33 gun was fitted (sIG 33/1) on the the hull of a repaired StuG III. This time the fighting compartment was completely enclosed and a MG 34 was mounted on a ball mount on the right side of the superstructure.
The sIG 33/1 gun was offset to the right side. It was capable of traversing 3° left and right, elevating 25° and depressing 6°. 30 rounds of ammunition was carried internally.
There is some confusion as to when the initial order was placed., but all the vehicles were built by Alkett.
According to Chamberlain and Doyle, Alkett was ordered in July 1941 to convert a dozen Sturmgeschutz III Ausf. E chassis and that these were finished between December 1941 and January 1942 - but not issued. On 20 September 1942, another dozen Sturmgeschutz IIIs were ordered to be converted, and the existing vehicles were rebuilt (Encyclopedia of German Tanks of World War Two).
Trojca and Jaugitz contend that all twenty-four were built starting in September 1942 from repaired Sturmgeschutz III Ausf. B, C, D and E chassis (Sturmtiger and Sturmpanzer in Combat)
The first dozen were delivered without the Scherenfernrohre 14 Z (scissors periscopes).
Deployment The first dozen were delivered by the end of October 1942 and assigned to Sturmgeschütz-Abteilungen 177 and 244, then fighting in Stalingrad.
The remaining twelve vehicles were intended for Sturmgeschütz-Abteilungen 243 and 245, but at the time of delivery the Russians had already surrounded the city. Instead, the vehicles were formed into Sturm-Infanterie-Geschütz-Batterie/Lehr-Bataillon XVII.
The battalion was assigned to the 22nd Panzer Division as the Germans attempted to break through the Russian encirclement of Stalingrad. The 22nd Panzer was virtually wiped out in the fighting.
On 11 April 1943 and the battery with seven remaining Sturminfantriegeschützwas assigned as the Sturm-Infanterie-Geschütz-Batterie/Panzer-Regiment 201 (also known as 9. Kompanie/Panzer-Regiment 201) in the 23 Panzer Division. The last strength report to mention them lists five vehicles remaining in September 1944.