Sunday, March 29, 2015

Sturmgeschütze (Assault Guns) I

After specification had been completed for German tank designs the infantry demanded an armoured close-support vehicle. Inspectorate 4 in their memorandum 449/36 g.Kdos of 15th June 1936 therefore asked the Army Weapons Department to produce an "armoured artillery close-support weapon for infantry and anti-tank purposes". The firm chosen to develop the chassis and carry out production was once again Daimler-Benz, while Krupp were made responsible for installing the guns.

The armoured vehicle duly evolved was armed with the 7.5 cm L/24 gun. The low silhouette demanded meant that the main armament was not mounted in a revolving turret but directly in the hull. The "assault guns" proved themselves to be extremely valuable in close support of the infantry and later, with heavier armament, in an anti-tank role. The chassis of the Pz Kw III tank was used as a basis for the vehicle because it was able to take the probable total weight of 20.2 tons. The specified armour thickness was 10 to 50 mm. Four men formed the crew.

An initial series of 30 vehicles was scheduled to go into production during February 1940. Troop trials continued throughout 1940 and five "assault guns" on Pz Kw III Ausf F chassis (S/ZW type) took part in the campaign in France. The production contract was signed in July 1940 and output was scheduled to reach 50 machines per month by September 1940. The official designation was "Gepanzerte Selbstfahrlafette für Sturmgeschütz 7.5 cm Kanone (Sd Kfz 142), (ref D 652/41 of 1st April 1943)". The model "A" version of the assault gun had the Maybach HL 120 TR engine and was fitted with the Maybach Variorex pre-selector gearbox -with 10 forward speeds and one reverse.

When production began these vehicles were assembled exclusively by AIkett. MIAG also participated in StuG III production from February 1943 to March 1945. Daimler-Benz also started building them in 1943.

Firms which supplied armour plate for these vehicles were: Brandenburgische Eisenwerke of Brandenburg, Harkort-Eicken of Hagen, Deutsche Edelstahlwerke AG of Hannover, and Bismarckhütte of Upper Silesia.

In 1940 184 StuG IIIs were produced. The monthly production average was 30 by 1st November 1940. During 1940 and 1941 StuG III models B to E came into service. These were fitted with the Maybach HL 120 TRM engine of 265 hp. A variable six-speed Aphon synchromesh gearbox type ZF SSG 77 was installed in these models. A few detail alterations were made in successive models.

For the short 7.5 cm Assault Gun 37 44 rounds of ammunition were carried but no machine gun was fitted for local defence. During 1941 548 vehicles were built. The monthly production figure of 40 machines, which had been decreed in 1941, was in fact reduced because of the increased numbers of Pz Kw III tanks which diverted chassis from assault gun production.

On 28th September 1941 Hitler demanded that assault guns be uparmoured regardless of the increase in weight and the reduction in speed. The machine was also to carry a gun with a longer barrel and of increased muzzle velocity. An instruction to this effect was issued by the Ordnance Department (No OKW/002205/41 g.Kdos), naming Daimler-Benz, 'once again, as the firm responsible for the chassis and selecting Rheinmetall-Borsig for fitting the new gun and for the superstructures. The vehicles were first shown to Hitler on 31st March 1941 with the hint that mass production could not begin before February 1942.

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