The SU-122 Assault Gun
This is the initial version of my article on the SU-122 Assault Gun. Any feedback will be appreciated.
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The SU-122 Assault Gun
Weight 30 900 kg
Length 6.95 m
Width 3.00 m
Height 2.32 m
Gradient 35 degrees
Gradient, side 25 degrees
Ground clearance 38 cm
Vertical step 76 cm
Trench-crossing 249 cm
Fording 130 cm
Track width 50 or 55 cm
Track ground length 372 cm
Ground pressure 11.8 to 11.9 psi
Track Gauge 247 cm
Steering mechanism: Clutch-brake
Engine and transmission:
W-2-34 24.87 liter 12-cylinder 4-stroke Diesel engine
500 hp at 1800 rpm, max torque 220 kgm at 1100-1200 rpm
Overhaul interval 300 to 400 hours
Rear sprocket drive
Sliding mesh gearbox with four gears forward, one gear reverse
Electrical starter with compressed air backup starting systems
Max speed 55 km/h on road, 25 km/h off-road
Range 300 km on road, estimated quarter to half that overland
Fuel capacity: 455+473 liters external fuel
Fuel consumption: 152 liters per 100 km on road, estimated 300 to 450 liters per 100 km off road.
Armor (mm@degrees) Front Side Rear Top/Bottom
Gun Mantle 65 – – –
Superstructure 45@40° 45@70° 45@50° 20@0°
Hull 45@30° 45@90° 45@45° 20@0°
121.9mm M-30S L/22 howitzer m/1938
Shell weight 21.76 kg
Muzzle velocity 515 m/s for HE round, estimated
Maximum range 9800 meters
Fire rate, shots/min: 2 to 3, estimated
Elevation -3 to +26 degrees, traverse 10 degrees left, 10 degrees right
HE shell OF-462
HEAT shell BP-460A
9R tank radio
5 W output, modular AM transmitter-receiver with preset channels
Range about 8 km while moving, about 20 km using morse key.
Connected to crew’s soft tanker helmets
The Red Army encountered German Sturmgeschutz assault guns for the first time in 1941. The advantages of assault guns were that they were less expensive to produce than tanks with rotating turrets and that a larger gun could be fitted onto the same chassis. The Soviet Union was struggling with raw material shortages which made assault guns an attractive proposition.
At a time when the average tank gun was still in the 76mm caliber range, the Russians brought the full firepower of a direct-firing 122mm howitzer onto the battlefield in the form of the SU-122. Built on the reliable and battle-tested T-34 m/1942 chassis, the howitzer had excellent mobility and could move at the same pace as other armored units.
The SU-122 had a crew of five. The driver sat in the front, on the left side of the gun. He steered the tank with steering sticks and the pedals were arranged in the fashion of conventional family cars. The T-34 suspension, a development of the Christie suspension used in the earlier BT series of light tanks, gave a relatively smooth ride and, coupled with the powerful diesel, excellent cross-country performance. The tracks had a life of about 2500 to 3000 km. The tank was easy to steer and the controls were light, though the driver’s seat was very uncomfortable. For visibility, the driver had a small hatch in the front glacis which was equipped with a vision port. The hatch was not large enough to be used as an escape hatch.
The gunner was seated behind the driver. He could aim the howitzer through his telescopic gunsight but was also provided with a vision port towards the front and a pistol port towards the left. In addition, there was a non-rotating cupola with vision ports toward the front and both sides which could presumably be used by either the gunner if he left his seat or by loader #1. The vision ports on the cupola could be opened and closed individually.
The first loader stood behind the gunner. Presumably he also had a folding seat for use during travel. Aside from the cupola mentioned previously, he had no view outside the vehicle.
The second loader stood on the other side of the fighting compartment. There was a large, foward-opening hatch which was used by the whole crew above his head, which provided his only view outside the vehicle, and that only if the hatch was open. Two loaders were needed to load the main shell and the required powder charges.
The commander sat in the front on the right side of the vehicle. He had a periscope with 2.5x magnification which could rotate 360-degrees, and a vision port and a pistol port facing toward the right. It is likely that he also acted as the tank’s radio operator for the 9-R radio, a reasonable set by Soviet standards. Of course due to shortages many SU-122s were probably sent into combat without radios.
The assault gun’s sole weapon was the M-30S howitzer, a development of the model 1938 howitzer used by the Red Army’s field artillery units. The huge piece made the insides of the vehicle extremely cramped. The bulk of the gun also manifested in a considerable overhang on the front of the vehicle, which may have had an impact on cross-country performance.
The SU-122’s gun was normally only used for direct fire. The howitzer was separately loaded, which meant that the shell was placed first into the breech, followed by a shell casing filled with powder charges, eight of which (four 100 and four 330 gram charges) made up the full charge and propelled the shell to the full 515 mps muzzle velocity. The breech was similar to those of other Soviet howitzers, it was manually rotated to open or close, with about ten revolutions of the handle being necessary.
The standard HE fragmentation shell contained 3.67 kg of explosives and was a devastating weapon against infantry, field emplacements and soft-skinned vehicles. Upon impact it shattered into 2000 to 2500 fragments with an initial velocity of 1000 to 1500 meters per second.
Most sources say that the HE shell was ineffective against armor but others claim that it nevertheless caused considerable damage due to the shock of the impact which caused a spalling effect inside the target tank. However that may be, the Russians decided to put a HEAT round into production for the howitzer, with the designation BP-460A. Apparently the round was not of high quality and it did not make the SU-122 an effective tank destroyer. No penetration data for either round seems to be readily available. At any rate the howitzer’s low muzzle velocity undoubtedly made hitting moving targets a difficult proposition.
The howitzer had no fume extractor in the barrel so much of the smoke and debris was sucked into the turret when the breech was opened. A ventilator with fans was located on the ceiling near loader #1’s position.
The SU-122 was first fielded in early 1943. At first the Red Army created self-propelled gun regiments which consisted of four batteries of SU-76 and two batteries of SU-122, each battery consisting of four self-propelled guns. From spring 1943 onwards, SU-122s were concentrated in medium self-propelled gun regiments, now equipped with 16 SU-122s and one T-34 command tank.
Production of the SU-122 continued until 1944, about 1100 being built.