SU-12 (1933)
Self propeller Howitzer, 1935-41, 100 made
The level of desperation of the Soviet Army in the autumn 1941 led to numerous ad hoc solutions being devised as weapons carriers, especially when regular armoured vehicles were missing in some categories, like artillery support. The SU-12 at the contrary was designed already in 1933 and produced until 1935 as a self propelled short barrel howitzer combining a 76 mm regimental gun M1927, shielded, placed on the flatbed of a 2x6 GAZ AAA standard truck. It was improved and produced again in 1941 as the SU-1-12 with a total of 99 made which saw action in the battles at Lake Khasan and Khalkhin-Gol River in the far east as well as in the Winter War in Finland.
Development
The SU-12 (here) and SU-1-12 were Soviet self-propelled artillery vehicles based on the Moreland and GAZ-AAA trucks chassis respectively. Both had the same short-barreled 76.2 mm gun model 1927 on a pedestal mount installed on the flatbed. Developement started in 1933 and was mass-produced in 1933-1935. Originally the request came in the 1920s when the Red Army ironing out its deep battle concept saw the need for a motorized self-propelled artillery unit. Troops still had a older Russo-Balt type T self-propelled guns from before the revolution, sporting a M1914 76.2-mm Lender anti-aircraft gun. But they proved underpowered and no longer suited the military. The main issue was that the chassid production depending on foreing components which were embargoed after the revolution. There were no longer spare parts either. They were rapidly wearing out.
There was no suitable replacement for this chassis and the Lender gun was not only suited for the nexw role envisioned and it was alrteady seen as obsolete. Work started again on a replacement in 1924 under N.M. Filatov, creator of Russian armored cars during the First World War such as the
Garford-Putilov. The chairman of the gunnery committee of the Red Army proposed a new self-propelled gun using a FIAT truck chassis, to be armed with the M1913 76.2-mm field gun, with a shortened barrel to reduce recoil and stress on the chassis.
However, the project did not receive due support and it was feared that the chassis could not obtained from abroad, or at least in 1924. In 1929, with the adoption of the "tank-tractor and protected armament system of the Red Army" program, development resumed, only to encounter a new specific problem as the Red Army command wanted a new "universal guns" which was widespread in Europe at that time. It was to be usable by troops and to be mounted on an SPG as well, even an aircraft. This led to a new three-year delay and ultimately the program was cancelled by November 1932. A return to more specialized ordnance was made evident in a letter to generalissimo M.N. Tukhachevsky:
...Mechanized troops need more mobile lightly armored guns and howitzers, while the infantry needs well-armored installations that can be used to provide cover from enemy fire... It is enough to have a regimental or divisional gun of 76.2 mm caliber with a firing range of about 2000 meters...
In mid-1933, a meeting was held with at the highest level of the command staff with the People's Commissars of Industry and it was decided to create a universal chassis for the development of self-propelled guns usabled either for the support of infantry, mechanized units, cavalry and AA defence as well. The Leningrad Kirov Plant received technical specifications, and developed the vehicle in a very short time. Tests of the new vehicle, the SU-12, started in late summer-early autumn of 1933, showing great results. It was thus accepted into service and launched into mass production... Only to be stopped after the 48th vehicle.
Indeed, the Kirov plant used the chassis of the American Moreland truck, initially used as a base. However relations with the USSR changed and exports were restricted, leading to the chassis to be unavailable as well as associated spare parts. The Kirov plan than turned its attention to the GAZ-AAA truck chassis, until mid-1935 until cancelled again, and not only when the war started as shown in some soutces. Thus, 51 more SPGs were manufactured for a grand total of 99 vehicles. To mark the difference, they were named SU-1-12. In between, changes and improvements were made to the design such as the shape of the gun shield, roof protection and rear of the driver's cabin. The gun platform was also modernized.
Design of the SU-12
General layout
The SU-12 and SU-1-12 were self-propelled artillery guns on a truck chassis with the artillery system placed in place of the cargo compartment. The crew of 4 comprised the commander, gunner, loader and driver. Initially, it was planned to produce the it on the GAZ-AA truck chassis, the production of which was launched in 1932 in Nizhny Novgorod. However, it soon became clear it could only withstand even the installation and fire of a light gun, more than 45 mm. Designers settled on the more robust Moreland truck, a number of which were purchased in the early 1930s from the USA for the needs of the Red Army. It had a 6x4 wheel arrangement for greater loads. The launch of the production of a domestic truck with a similar wheel arrangement and the GAZ-AAA, whicvh was one chosen afterwards for the SU-1-12.
During its construction changes and modifications were made to the chassis design, related to the installation of of the regimental gun. In place of the cargo compartment it had a special metal platform without barriers on which the pedestal mount was bolted on. The platform above the flatbed also strengthened and lengthened the frame and it was supplemented with a towing hook, a spare wheel frame, a front flooring, 2mm vertical steel reflector protecting the cabin from the ingress of powder gases and rectangular window for communication between the driver and gun crew. If necessary, the window was closed from inside the cabin and it had a steel shutter.
There were two loading boxes for 18 shots each attached to the rear wall of the reflector as well as spare parts kit. Already during serial production, it had additional protection for the roof and rear driver's cabin and the gun platform was also somewhat modernized on the SU-1-12.
Engine and performances
The SU-12 was based on the Moreland truck, possibly the 1925 TX6 model powered by a Continental 14H engine. No info on the exact type. As for the SU-1-12, it was based on the better known
GAZ-AAA, it had semi-elliptical springs, was powered by a GAZ M-1, with carburetor rated for 50 hp, top speed 60 kph, Range 370 km on road max. The rear train comprised two axles with double wheels so eight in all to support the weight. The GAZ AAA could ford a depth of 0.82 m, cross an obstacle 0.75 m high, gap a 2 m ditch with a ground pressure of 0.68 kg/cm2.
Armament
The 76.2 mm regimental gun model 1927 was used as main armament, available in large quantities and quite satisfactory with a small size making it suitable for a truck. The barrel and recoil system were slightly modified to reduce the recoil from 1000 to 500 mm. It was installed on the platform using a specially designed pedestal mount. It ensured all-round fire but not forward fire as the cabin went against the elevation angle with a dented roof due to the blast. Traverse was limited to 270° and stoppers were installed on the pedestal. It was rotated manually, with a brake to fix the pedestal in a single position. The side windows of the cabin had some angles were lowered avoid destruction by blast damage.
The rate of fire was 10-12 rounds per minute. It could be fired both straight back and along the side with experiments firing on the move, greatly reducing accuracy. A simple optical sight was used and the gun's a monocular artillery sight. Ammunition comprised 36 rounds (other sources: 34 rounds) in in shell boxes on the rear wall of the cabin reflector, including 18 high-explosive fragmentation, right box and 18 shrapnel in the left box. The gun elevation was from -5°/+25° on the SU-1, 270° traverse.
Protection
The SU-12 armor was limuited to the gun shield and on the Moreland truck, completely absent. At first a U-shaped vertical box-shaped armor shield was installed on the pedestal, made of four armor plates 4 mm thick welded together. The shield partially protected the gun crew and mechanisms from rifle fire and shpanel. On the SU-1-12 it was modernized with a better shaped box, with more complex sloped shape and wider. The upper part was angled 25° with an an embrasure for the gun. To its left were two windows closed by latches with a reflector and sighting tube for the optical sight. It was attached to the rotating base of the pedestal.
An additional 4-mm shield-mask could cover the embrasure. The shield was gled to 80°, here with a lower part bent forward by 10°. This was for a much improved shield, for better protection all around of the gun crew.
⚙ SU-12 specifications |
| Displacement | 6 tonnes |
| Dimensions | 5,61 x 1,90 x 2,325m |
| Suspension | semi-elliptical springs |
| Propulsion | GAZ M-1, carburetor 50 hp |
| Speed | 60 kph |
| Range | 370 km |
| Armament | 76.2 mm/16.5 regimental gun model 1927, rifled (36) |
| Protection | Shield front 4 mm, mantlet 4 mm, sides 4 mm |
| Payload | |
| Crew | 5 (driver, Cdr, 1 gunner, 2 loaders) |
The SU-12 in service
After factory and field tests in mid-1933, decision was made to launch the self-propelled guns into "mass" production. In the autumn, an experimental battery was sent to the 11th Mechanized Brigade in Ukraine for field tests in realistic conditions. Based on theses results the Red Army command decided to integrate the vehicle in the newly formed mechanized brigades as direct, mobile fire support for infantry and tanks.
Thus, the SU-12s were included in mechanized and later tank units, albeit in small numbers. However it was mostly dispersed among various mechanized units by penny packets of 3-4 vehicles. By mid-1938 the SU-12 based one the Moreland chassis ended in tank units of the Leningrad, Moscow, Belorussian, and Kyiv military districts. The SU-1-12s based on the GAZ-AAA chassis ended with the Leningrad, Moscow, Kyiv, and Transbaikal military districts and Special Red Banner Far Eastern Army. In 1938, more than a third owere already considered worn out and in repairs. In total 40 modifications were recorded, mainly in the Kiev, Moscow, and Zabaikalsky Military Districts after the Moreland truck based SU-12 were removed from service.
With the Soviet-Japanese confrontation at Lake Khasan in the summer of 1938, combat-ready self-propelled guns were only the remaining SU-1-12s pressed into the final stage of operations and on July 31, 1938, SU-1-12s from the 2nd and 3rd tank battalions, 2nd mechanized brigade took part in the battles at the Zaozernaya and Bezymyannaya heights. Each battery was assigned to a tank battalion and had four SU-1-12s, two SU-5-2s (T-26 chassis as complement). Eight SU-1-12s and four SU-5-2s thus were actived on July 31, firing 248 76-mm and 23 122-mm shells, a significant support to the BT-5 and T-26 from the 2nd mechanized brigade, with no losses. Overall their first combat use was deemed "very successful".
Next, SU-1-12 took part in the battles near the Khalkhin-Gol Rivee, summer 1939. The only unit of that kind was the 32nd Mechanized Brigade transferred to Mongolia in 1937 to reinforce Soviet troop, with just four SU-1-12. Record unknown. Next, they were used to a limited extent in the Winter War against Finland in 1939, with the 33rd Separate Reconnaissance Battalion operating on the Karelian Isthmus. As of March 9, 1940, it was composed of two T-27 tankettes and two SU-1-12. As of December 1, 1940, the Red Army tank units formally included three SU-1-12s at the Transbaikal Special Military District. They were written off in 1941-1942.
Still, that kind of truck based artillery was considered a success" through testing and operation. It was deduced that a self-propelled gun was a fairly effective and mobile weapon already in the mid-1930s, with the 76.2 mm regimental gun model 1927 remaining adequate to requirements. As an anti-tank weapon it was still used until 1942. The firing angle was also satisfactory and the ability to fire immediately after stopping, without peparation and to be on the move were also much appreciated. The Moreland chassis did not however fully meet the requirements due to the general burden and firing stressed on the unmodified rear axles. Its off-road cross-country ability was significantly reduced as well and the GAZ-AAA base did not improved it much.
Complaints concerned the poor protection of gun servants, overall extremely high vulnerability. In 1935 maany advocated for a more advanced vehicle than a self-propelled gun based on a tank chassis and the lack of suitable chassis forced alternatives. The advantage of readiness and low cost and general convenience was hamped by poor cross-country limits and protection, below acceptable limits. Several high-explosive shells falling near enough could wide out the entire unit. Sniper fire also. In the end the Red Army recoignised this as a temporary measure until more advanced self-propelled units entered service, like the Su-76.
Tweaking with the T-26 tank chassis and tractors enabled the appearance of more advanced SPGs later, and production of SU-12 was never resumed after 1938. Because of this, the USSR started operations in the summer 1941 without any self-propelled guns in service. But they were definitively on the menu as the Battle at Lake Khasan showed their efficience with skillful use.