The combat experience of the initial period of the Great Patriotic War proved the need for self-propelled artillery to accompany tanks in battle, and in October 1942 the State Defense Committee decided to begin work on the creation of a self-propelled artillery vehicle (SPG) based on the T-34 tank with a 122 mm M-30 howitzer of the 1938 model, which was adopted by the Red Army in December (!). Of course, the hastily created vehicle was not without its shortcomings, which had to be corrected right at the start of mass production. The resulting self-propelled gun, which had the factory designation U-35 (SU-35) and the army designation SU-122, went into mass production at the Ural Heavy Engineering Plant (UZTM) at Sverdlovsk. Throughout the entire period of serial production of the SU-122, which lasted from December 1942 to August 1943, there was a continuous improvement in the quality and manufacturability of its production: the work carried out to improve the production and assembly technology made it possible to significantly reduce the labor costs for the production of the machine.
Structurally, the SU-122 was a hull of the T-34-76 tank with the control and fighting compartments combined in a casemate. This compartment housed weapons, seats for the driver, commander, gunner, and two loaders, ammunition, controls, control instruments and a radio station. The commander also served as the radio operator and air guard. On the roof of the cabin was a cupola with three inspection ports for a periscope sight and a hatch.
The engine and transmission compartments, as well as the chassis, were unchanged from the T-34.
This self-propelled gun was armed with a 122 mm M-30S howitzer. The pinned upper carriage of the 122 mm field howitzer of the 1938 model was placed in the socket of a special cabinet mounted in the front part of the hull bottom. The swinging part of the howitzer was attached to the axles of the machine, and the barrel, cradle, recoil devices, sight and guidance mechanisms were taken over as standard without any changes. The need to armor the swinging part made it necessary to strengthen the spring balance mechanism, which was done without changing its dimensions. The direct firing range of the gun was 3600 m, and the maximum indirect firing range was 8.0 km. The shells used were mainly high-explosive separate charges OF-462 weighing 21.76 kg (with an initial velocity of up to 515 m/s). Against tanks, cumulative projectiles of the BP-460A type (13.34 kg, 335 m/s, armor penetration 120 mm) could be used.
In total, UZTM built 638 SU-122s. Self-propelled guns of this type were delivered to self-propelled regiments (a mix of SU-76s and SU-122s), and from April 1943 — to medium self-propelled regiments (SU-122 only). The regiments were supposed to be attached to tank and mechanized corps but were often used in support of the infantry.
SU-122s took part in the Battle of Kursk. Together with the heavy SU-152s, they proved to be one of the few combat vehicles that could withstand German innovations, so from the second half of 1943, SU-122s were often used as antitank weapons. At the beginning of 1944, they were replaced by new self-propelled guns of the SU-85 type, better suited for fighting tanks, but the SU-122 continued to be used in the regiments where they were retained. It is interesting that at the same time, the commanders tried not to send them for repairs (otherwise they would be replaced by SU-85s), but to repair them on the spot, so that a certain number of SU-122s even reached Berlin.
Used sources:
1. M. Baryatinsky “Self-propelled guns based on the T-34 tank,” magazine “Armor Collection” No. 01 2000
2. M. Svirin “Stalin’s self-propelled guns. History of Soviet self-propelled guns 1919-1945" 2008
3. G.L. Kholyavsky "Complete encyclopedia of tanks of the world 1915 - 2000" 1999
Assault gun SU-122 was produced at Ural Heavy Machinery Factory (UZTM) in Sverdlovsk from the end of December 1942 till August 1943 with 640 units built in total.
It used Т-34-76 tank chassis, but the crew compartment has been completely rebuilt and the original turret was replaced with 122 mm M-30S howitzer. The suspension, engine compartment and the total weight of the vehicle remained the same, although the front armor slope was reduced. The assault gun was equipped with panoramic non-recoiling gunsight capable of direct fire for the gunner and PTK-5 panoramic visor for the commander.
The assault guns made in early May 1943 like the one represented in the sim had a new traveling lock for the gun, different gunner cupola shutter mechanisms and a small hatch that made access to the right track tightener easier.
Unladen weight: 30900 kg.
Length: 6.9 m.
Width: 3.0 m.
Height: 2.2 m.
Clearance: 400 mm.
Engine: V-2 diesel.
Maximum power: 500 HP at 1800 RPM.
Maximum RPM: 1900 RPM.
5 speed gearbox.
Maximum road speed:
1-st gear: 7.4 kph.
2-nd: 15.9 kph.
3-rd: 22.4 kph.
4-th: 34.1 kph.
5-th: 54.0 kph.
Reverse: 8.4 kph.
Maximum offroad speed: 31 kph.
Fluids:
Internal fuel tanks capacity: 460 l.
Engine oil system capacity: 80 l.
Summer engine coolant: 95 l. of water
Winter engine coolant: 95 l. of 50% ethylene-glycol
Endurance range: 300 km.
Maximum oil consumption: 9 l/h.
Armour:
Front: 45 mm.
Sides: 45 mm rolled armour.
Rear: 45 mm rolled armour.
Roof: 20 mm rolled armour.
Bottom: 20 mm rolled armour.
Bottom above tracks: 20 mm rolled armour.
Gun mantlet: 45 mm rolled armour.
Main gun: rifled, 122 mm M-30S, separate loading.
Barrel length: 22.7.
Elevation: +25°..-3°.
Azimuth: +10°..-10°.
Ammo: up to 40 rounds.
Usable rate of fire: 3 rounds per minute.
Turret drive: mechanical.
Gun ammunition:
OF-462 high explosive (HE): 21.79 kg, 515 m/s, 3.67 kg explosives.
Gunsight settings
(Distance - point number of "ДГ полный" scale):
0000m - 000
0200m - 004 3200m - 064 6200m - 124
0400m - 008 3400m - 068 6400m - 128
0600m - 012 3600m - 072 6600m - 132
0800m - 016 3800m - 076 6800m - 136
1000m - 020 4000m - 080 7000m - 140
1200m - 024 4200m - 084 7200m - 144
1400m - 028 4400m - 088 7400m - 148
1600m - 032 4600m - 092 7600m - 152
1800m - 036 4800m - 096 7800m - 156
2000m - 040 5000m - 100 8000m - 160
2200m - 044 5200m - 104 8200m - 164
2400m - 048 5400m - 108 8400m - 168
2600m - 052 5600m - 112 8600m - 172
2800m - 056 5800m - 116 8800m - 176
3000m - 060 6000m - 120 9000m - 180
BP-460A high explosive anti-tank (HEAT): 13.34 kg, 335 m/s, 120 mm.
Gunsight settings
(Distance - point number of "ДГ третий" scale):
0000m - 000
0200m - 004 1200m - 026
0400m - 008 1400m - 032
0600m - 012 1600m - 037
0800m - 017 1800m - 042
1000m - 022 2000m - 047
Gunsights:
PG gunner panoramic periscopic sight, field of view 10.5°, allows indirect fire.
PTK commander panoramic periscopic sight, field of view 26°, for target designation and observation.
Radio equipment:
VHF 9-RM transceiver.
3 intercom terminals.