SOV - SG-122 (A) (122mm samohybná houfnice)

On 19.10.1942, the Soviet authorities ordered the development of a self-propelled howitzer of 122 mm caliber. Work on such a weapon began at Plant No. 592 and (possibly) UZTM. The prototype was completed at Plant No. 592 in late 1942. Based on a platform of captured German medium tanks Pz.Kpfw. III or StuG III (Soviet documents speak directly of "артштурм", the Russian name for the StuG assault guns). A 122 mm howitzer M-30 Model 1938 placed in the fixed superstructure. Design work on the SG-122(A) "A"="artyshturm" project was led by A. Kaštanov (A. Каштанов). The first prototype was to be built on the StuG III Ausf. C or Ausf. D. A simple box superstructure was created and the aforementioned 122 mm howitzer was mounted in it. The frontal armour was 45 mm thick, the side and rear armour ranged from 25 - 35 mm. The crew consisted of 5 persons (commander/radio operator, driver, gunner and two loaders). The crew entered the vehicle through two hatches located on the roof of the superstructure. The prototype was thoroughly tested (480 km and 66 rounds fired). The test committee had reservations about the self-propelled vehicle. They were mainly related to the lack of passability through muddy terrain, poor centre of gravity and consequently too much stress on the front part of the chassis, the excessive workload of the vehicle commander who had to perform too many duties, insufficient fuel capacity, the machine had no firing holes for firing small arms of the crew, insufficiently tight connection (welding) of the superstructure with the hull part and insufficient ventilation of the fighting compartment during firing. The production plant proceeded to modify the design. It was decided to use not only the chassis of the German assault guns StuG III, but also the platforms Pz.Kpfw. III. To lighten the weight, the thickness of the front armour was reduced to 35 mm, the sides and rear were 25 mm thick. The layout of the crew positioning was changed and the commander received new observation instruments. Gunnery ports for firing the crew's personal weapons (the same as in the SU-76i) were fitted. The howitzer was also lightened. By fitting external fuel tanks, the range of the machine was increased. The radio station was moved from the port side to the starboard side. The sides of the superstructure were sloped to 10-20°. The gun shield was also modified. This modified machine was ready for mass production, but at that time a "competitive" self-propelled howitzer SU-122 was completed, which was being worked on by the UZTM plant. Only a small batch of SG-122(A) were produced. There is controversy about the amount of machines built. Russian sources themselves say 8 were completed on the StuG III platform by the end of 1942 (joint numbers with SU-76i). Two more units were to be built on the Pz.Kpfw. III and Pz.Kpfw. The data speak of the appearance of three SG-122(A) on the test polygon in [url=/topic/view/123859]Sverdlovsk (as of 15.11.1942, two of them built on the StuG platform). On 5.12.1942, one piece was to be built on the Pz.Kpfw. III was sent to the Gorochovets polygon for joint tests with the competing SU-122.
The production plan was cancelled and the produced machines served out their service life in training units.
Alternative numbers of machines produced are offered by the publication and from Eksprint, where 21 SG-122(A) are said to have been built.

Soviet medium self-propelled guns 1941-45 - published by Ekssprint, published in 2005, ISBN 5-94038-079-4
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