A howitzer on the T-34 chassis
The SU-122 was the first major variant of the successful T-34 chassis. After the first German Sturmgeschütz assault guns were seen in operations, an order was issued in April 1942 to several design bureaus to devise plans for a prototype SPG. Many heavy guns were tested in the process. It was seen the assault gun formula amassed the advantages of a cheaper, easier produced vehicle with the use of heavier guns, albeit with the disadvantage of having to turn the entire vehicle to aim in combat. In the end, both 122 mm (4.8 in) and 152 mm (5.98 in) field howitzers were retained. Only the 122 mm (4.8 in), developed by F. F. Pietrow’s design bureau as the M-30S, was found suitable for a medium tank chassis.
Development of the SU-35
In fact, before any T-34 adaptations were produced, ten captured German Sturmgeschütz IIIs served as testbeds for the adaptation of the M-30S, under the name of SG-122. Deemed too complicated and difficult to maintain, they were phased out in favor of a proper Russian mass-built SPG. The most obvious option back then was the T-34. This choice was made by Uralmashzavod Uralsky Machine Building factory (UZTM), headed by chief engineers Kurin and Kusjin. They then developed the U-34, a long barrel 76 mm (3 in) gun armed turretless version based of the T-34 chassis.
They decided not to waste time, thus using the gun mount of the SG-122 and the hull, chassis, engine and transmission of the T-34. This led to the development of the final U-35, during the summer of 1942. After difficult trials led during the winter, the SU-35 was officially approved for production in limited numbers because of many flaws, but larger orders came after better trials and it was renamed into the SU-122.
Specifications and production
The Samokhodnaya Ustanovka 122 mm (4.8 in) or, in short, SU-122, was not at first a satisfactory model. The gun elevation was poor (initially designed for −3° and +26° with a 10° of traverse), the crew compartment was poorly ventilated and the crew was badly placed. All these defaults were corrected, as well as other minor modifications for mass-production. A slightly less sloped glacis (still 45 mm/1.77 in thick, almost 80 mm/3.15 in effective), simplified slits, rearranged fighting compartment layout, an increase in ammunition carried and a more efficient commander periscope.
The SU-122 was 70 cm (2.3 ft) lower, which meant it was more difficult to hit than an average T-34. The gun itself was protected by its own massive mantlet, encapsulating the receiver, fume extractor and a muzzle brake, protruding from the glacis. There were no auxiliary weapons, the crew being only protected by their own automatic Makaroff revolvers. Production began in December 1942 and went well until early 1944.
The SU-122 in operations
The SU-122 was not meant to deal with other tanks, but only with German fortified positions, strongholds and ranged infantry support, which came at the right moment when the German army was in a full retreat behind successive defensive lines. After training, the crews joined the first active units in January 1943. These were the 1433rd and 1434th self-propelled artillery regiments, partially equipped with older SU-76 tank-destroyer models. The regiments were made of two batches of four of both models, led by a single SU-76 tank destroyer as a command vehicle.
The SU-122 were supposed to be covered by the SU-76. They joined the 54th Army near Leningrad and fought at Smierdny. Later, regiments were incorporated in assault squads comprising many models, the SU-122 being posted at the rear, 200 to 600 m (219-656 yd) behind the advancing columns. After war experience, and the reorganization of the mixed regiments, they all ended with independent brigades (“medium self-propelled artillery regiments”), equipped uniformly with SU-122s, and affected to various parts of the front were they were needed. But in 1944, they were already being phased out by more capable SU-152 and SU-85 tank destroyers.
On several occasions, some SU-122s had to deal against enemy tanks, including the Tiger, especially at Kursk during the summer of 1943. They used their howitzer HE rounds to dislodge turrets and break tracks by brute percussion force. This same year, a new projectile was introduced in limited provisions especially to deal with these targets, the BP-460A HEAT. But both this and the classic HE were only efficient at close range, in a quite dangerous way. Losses were huge and a handful fell into enemy hands, as the Sturmgeschutz Beutepanzer SU-122(R).
Variants and legacy
The 122 mm (4.8 in) M-30S howitzer was cumbersome and required three crew members to operate, including the commander. For these obvious reasons, a replacement was in line soon after the first action reports came back from the front. It was crossed with a parallel project, even before production started, of a more simpler and cheaper version. In April 1943, a prototype was built with a more compact and modern D-11 howitzer.
The commander was liberated from his task as loader, as the hull was enlarged and allowed an extra crew member to fit in the fighting compartment. The driver now had his own escape hatch. But the SU-122M was never put into production, the head of staff deciding to convert existing facilities to mass-produce the SU-85 tank destroyer instead. Another prototype, the SU-122-III, was issued an even lighter D-6 howitzer.
But, due to the unreliability of the artillery piece, this project was also dropped. The last attempt was to combine the SU-122 hull with the ball mantlet of the SU-85. But this was also halted. In fact, the real legacy of this self-propelled howitzer was to allow a relatively fast and successful conversion of the T-34 chassis, hull, engine, and transmission, ending with the SU-85 and SU-100 tank destroyers, one the greatest success stories of the entire Russian arsenal. Today a single SU-122 is shown on display at the Kubinka Museum (near Moscow).
Links on the SU-122
|Dimensions||6.95(oa) x 3 x 2.32 m
|Total weight, battle ready||30.9 tons|
|Propulsion||Klimov diesel V12, 493 bhp|
|Speed (road)||55 km/h (34 mph)|
|Range||400 km (248 mi)|
|Armament||122 mm (4.8 in) M-30S howitzer|
|Armor||Max 45mm (1.77 in)|
A first production SU-122, in March 1943.
An early production SU-122 in December 1942, Leningrad front, Smierdny region. By then, these were combined in small four-unit squads with four SU-76 tank destroyers. Two of these squads formed a battalion. Notice the washable white paint and definitive front wheels.
SU-122 at Kursk, July 1943. During the most desperate moments of this battle, some SU-122s fired at close range and sometimes successfully dislodged Tiger tank turrets. The sheer destructive power of a HE 122 mm (4.8 in) shell was in itself a potent force to be reckoned with.
A SU-122 at Kursk, July 1943, freshly arrived from the factory with a rather unusual sand livery over the usual olive green. Identification numbers were hand-painted, probably in the storage lot or directly over the transporting rail carriage.
A mid-production SU-122, winter 1943, with a rare improvised camouflage over the usual washable white paint. Also notice some roof sights and hatches painted in red.
A rare SU-122 in German serive. During the early year 1943, the Wehrmacht was still able to launch some localized counter-offensives on a rather dynamic, but mostly defensive front, with the initiative definitely into Russian hands.
During these events, both German and Russian tanks were disabled and captured by their respective adversaries.
There are few records of captured SU-122s, and even less photographic evidence, but they were probably camouflaged and flagged with a wide Balkan cross, and often swastika flags over the top.