In early 1942, Alkett was ordered to design and produce a new Sturmpanzer in cooperation with Krupp. Alkett would design the sloped armor superstructure containing a 15 cm howitzer. The superstructure was to be placed on a modified Panzerkampfwagen IV chassis modified by Krupp.
Since 1940 a number of attempts had been made to mount a 15 cm sIG 33 on a tank hull. These interm designs led to the developement of the SIG 33B with a fully enclosed fighting compartment mounted on a Panzerkampfwagen III.
The new Sturmpanzer IV was to be a production vehicle using a use the Panzerkampfwagen IV chassis and a 15 cm StuH 43 L/12 gun (a tank mounted version of the sIG 33 developed by Skoda) A prototype was produced in February 1943 and the new vehicle was designated Sd.Kfz.166, Sturmgeschutz IV mit 15cm StuH 43.
The 15 cm StuH 43 L/12 gun was mounted on a huge ball mount projecting through the front of the 100 mm superstructure armor. The vehicle weighed in at 28 tons which was a heavy load for the chassis and the cause of transmission problems. Oddly the Sturmpanzer IV was designed for close in combat in cities but lacked a close support machine gun until the late (4th series) production run.
Production of the first series of 60 vehicles began in April 1943. Fifty-two of these were built using new Panzer IV Ausf. G chassis and the remaining 8 from rebuilt Ausf. E and F chassis. Survivors, about half, were rebuilt beginning in December 1943; they were mostly rebuilt to 2nd series standards.
Production restarted in December 1943 of another 60 vehicles, using only new Ausf. H chassis, and continued until March 1944. The Stupa's baptism in combat during Operation Citidel (Kursk) proved that the driver's compartment was too lightly armored and it was reinforced. The gunner's hatch was removed and a ventilator fan was fitted, much to the relief of the crew. Internally-sprung, steel-rimmed road wheels replaced the front two rubber-rimmed road wheels in an effort to reduce the stress on the forward suspension that was only partially successful. 3rd Series
Production of the 3rd series ran from March to June 1944 with few changes from the second series. The Fahrersehklappe 80 was replaced by periscopes and the lighter StuH 43/1 was used.
4th Series The superstructure was redesigned in early 1944 for the fourth series, which used the chassis and HL120TRM112 engine of the Ausf. J, and was in production between June 1944 and March 1945. It featured a redesigned gun collar, as well as a general reduction in height of the superstructure. This redesign also introduced a ball mount in the front superstructure for a MG34 . The vehicle commander's position was modified to use the hatch of the Sturmgeschütz III Ausf. G, which could mount a machine gun for anti-aircraft defense.
Approximately 306 of all series were built.
Sturmpanzer-Abteilung 216 The first unit to take the Sturmpanzer IV into battle was Sturmpanzer-Abteilung 216. It was formed at the end of April 1943 and transferred in early May t0 Amiens to train on its new assault guns. It was organized into 3 line companies, each with 14 vehicles, and a battalion headquarters with 3 vehicles.
It arrived in Central Russia on 10 June 1943 to prepare for Operation Citadel, the German attack on the Kursk Salient. For this action it was temporarily assigned as the third battalion of schweres Panzerjäger Regiment 656 under the command of the 9th Army (Army Group Center).
It remained in the Orel-Bryansk area until its transfer to the Dnepropetrovks-Zaporozhe area at the end of August. Its vehicles were refitted there and it remained there until the Zaporozhe Bridgehead was abandoned on 15 October 1943. The battalion retreated to Nikopol where it helped to defend the German salient there until it was withdrawn back to the Reich at the end of December 1943.
The Allied landing at Anzio on 22 January 1944 caused the battalion, fully independent once more, to be transferred there in early February with 28 vehicles to participate in the planned counterattack against the Allied beachhead, Operation Fischfang. The operation failed, but the battalion remained in Italy for the rest of the war. The battalion still had 42 vehicles on hand when the Allies launched their Po Valley offensive in April 1945, but all were blown up to prevent capture or lost during the retreat before the war ended in May.
Sturmpanzer-Abteilung 217 Sturmpanzer-Abteilung 217 was formed on 20 April 1944 at the Grafenwohr Training Area from cadres provided by Panzer-Kompanie 40 and Panzer-Ersatz Abteilung 18, although it did not have any armoured fighting vehicles until 19 'Stupas' were delivered at the end of May.
It departed 1/2 July for Normandy. It detrained at Conde sur Noireau, over 100 miles behind the front lines. Many of the battalion's vehicles broke down during the road march to the front lines. The first mention of Sturmpanzer IVs in combat is on 7 August near Caen. On 19 August, the battalion had 17 Sturmpanzers operational and another 14 in maintenance. Most of the battalion was not trapped in the Falaise Pocket and managed to retreat to the northeast.
It had only 22 vehicles in October, which were divided between the 1st and 2nd Companies; the surplus crews were sent to Panzer-Ersatz Abteilung 18. It participated in the Battle of the Bulge only advancing as far as St. Vith. It was continually on the retreat for the rest of the war and was captured in the Ruhr Pocket in April 1945
Sturmpanzer-Kompanie z.b.V. 218 Sturmpanzer-Kompanie z.b.V. 218 was raised in August 1944. It was sent toWarsaw where it was attached to Panzer Abteilung (Fkl) 302. It remained on the Eastern Front after the Warsaw Uprising was suppressed and was eventually wiped out in East Prussia in April 1945. It was supposed to have been the cadre for Sturmpanzer Abteilung 218 in January 1945, but it was never pulled out of the front lines to do so.
Sturmpanzer-Kompanie z.b.V. 2./218 Sturmpanzer-Kompanie z.b.V. 2./218 was raised simultaneously with Sturmpanzer Kompanie z.b.V. 218, but was transferred to the Paris area on 20 August. Nothing is known of its service in France, but company personnel were sent to Panzer-Ersatz Abteilung 18 at the end of the year and were supposed to have been used in the formation of Sturmpanzer Abteilung 218. Sturmpanzer-Abteilung 218 Sturmpanzer-Abteilung 218 was ordered formed on 6 January 1945 with three companies with a total of 45 Stupas, but it received Sturmgeschütz III assault guns during February instead.
Sturmpanzer-Abteilung 219 Sturmpanzer-Abteilung 219 was originally to be formed from Sturngeschutz-Brigade 914, but thei was changed to Sturngeschutz-Brigade 237 in September 1944. In mid-September 1944 the brigade transferred to the Dollersheim Training Area to reorganize and re-equip. Only ten Stupas had been received when the battalion was alerted on 15 October to participate in Operation Eisenfaust, the German coup to forestall Hungary's attempt to surrender to the Allies. All the vehicles were given to the First Company and it departed for Budapest on the following day. Bomb damage to the rails delayed its arrival until 19 October, by which time it was no longer needed as a pro-German government had been installed. It was sent by rail to St. Martin, Slovakia for more training. The battalion was transferred to the vicinity of Stuhlweissenburg to relieve German forces trapped in Budapest. It remained in the vicinity of Budapest until forced to retreat by advancing Soviet forces.