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SU-1 76 mm self-propelled Assault Gun

At the end of 1930, in parallel with the work on self-propelled artillery mounts on the chassis of medium tanks T-24 and T-19, the chairman of NTK UMM Lebedev put forward similar requirements for consideration by the joint Soviet-German Technical Commission.

From the German side, Daimler-Benz undertook the design, from the Soviet side, the creation of self-propelled guns was supervised by the 4th section of NTC UMM and the 2nd section of NTK AU. It was assumed that the self-propelled gun will have the following characteristics:

• combat weight - up to 9 tons (for a divisional gun - 12 tons); crew - 3-4 people;
• armament - 76-mm regimental gun obr.1927, or divisional gun obr.1902;
• armor - 11-20 (15-30) mm;
• speed - 30-35 km / h;
• range - 180-200 km.

While the preparatory work was going on, it turned out that it would not be possible to get the chassis of medium tanks of Soviet construction in the near future. The serial production of T-24 at KhPZ was never organized, and the T-19 was considered too complicated and expensive to manufacture.

Instead of them the British Vickers infantry tanks and the American “cavalry” Christie M1928 were to be produced. At the same time, in 1931, the site of the divisional SAU had already been “upgraded” by the tank-tractor and auto-armor systems. The terms were “pressed” and the designers had to act on the basis of the prevailing circumstances.

After analyzing the existing hardware of the Red Army, a logical conclusion was drawn that the chassis of the Vickers tank, which in the USSR from an “infantry” reclassified to “light” and was designated first as B-26 and then T-26, could easily fit for the 76-mm self-propelled guns.

Since time was sorely lacking, some self-propelled units were designed “on the knee”, which made it more of an experimental machine. Actually, they did not have to make radical changes in the design of the T-26 tank model 1931.

The chassis, in relation to one side, consisted of eight double rubberized support rollers with a diameter of 300 mm (interlocked in pairs in four balance trolleys) suspended on sheet quarter-elliptical springs, four rubberized supporting rollers with a diameter of 254 mm, a guide wheel with a crank tensioning mechanism and a driving wheel front location with a removable toothed rims (pinching pin). Caterpillars 260 mm wide were made of chromium-nickel or manganese steel.

The mechanical transmission consisted of a single-disk main friction clutch for dry friction, a cardan shaft, a five-speed gearbox, onboard clutches, on-board gears and belt brakes located on the cases of the onboard clutches.

Only the hull has undergone significant changes. The lower part of it, down to the flank niches, remained the same, and the upper part was completely redone. Instead of a towed box and towers, a fixed four-sided wheelhouse was installed.

The side and rear armor plates were mounted vertically, and only the front sheet of the superstructure had a small angle of inclination. Along the sides of the cabin, doors were made for embarkation and disembarkation of the crew. On the roof was mounted a small non-rotating commander's turret with a round hatch and viewing slots.

The gun, which was a regimental cannon of the sample of 1927 (GAU index 52-P-323), was mounted on a cabinet borrowed from the Garford armored car. Although these machines were already decommissioned in combat effectiveness, they were not equal until the appearance of the BA-3, and individual design solutions could still serve for several years.

The gun itself was also upgraded. For installation on an ACS, the barrel rollback length had to be reduced to 500-500 mm (according to other data, to 750 mm), but this did not affect the initial speed of the shrapnel shot, which was still 381 m / s. It should be noted that the regimental gun obr.1927 was considered more likely a necessary measure, since its progenitor was a “short” weapon obr.1913.

It was difficult to use it as an anti-tank weapon, but for fire support of the advancing infantry and the fight against field fortifications, the power of a high-explosive projectile or a fragmentation shot was considered to be quite enough. The maximum penetrability of the vertically installed armor-piercing armor-piercing armor-piercing plate from a distance of 100 meters was 34 mm, and at a distance of up to 2000 meters, this indicator decreased to 24 mm. Accordingly, the same shortcomings were transferred to the tank gun KT-28, created on the base in 1931.

The assembly of the SU-1 self-propelled unit , carried out as soon as possible, led to a number of design flaws and flaws. In the first tests conducted in the autumn of 1931, the gun failed after the first shot and the installation had to be sent in for repair.

In addition, many caveats caused the design of the cabin, made of “raw” (non-armor) steel. In addition to the constrained working conditions of the crew, the cut-out for the installation of the gun was made “by eye” and therefore during the sighting of a DT machine gun (150–200 meters), bullets flew freely into the fighting compartment. It was decided to continue tests without weapons.

All work was carried out in a short time, and already in October 1931, the finished machine was transferred to the research artillery range on the Okhta field (Rzhevsky range) for testing. The haste of manufacturing the prototype has affected its quality and reasonable design. At the very first shots, the SAU gun failed, as the gun stand was not massive enough for the selected gun. After changing the design of the cabinet and repairing the instrument, the tests continued.

After 30 km, traveled off-road and rough terrain, the SU-1 showed that its driving characteristics are absolutely not inferior to the serial tank T-26. After the repair of the gun and the reinforcement of the installation, the ACS was again filed for fire tests during which 41 shots were fired from the spot and 3 on the move. Apart from one misfire, the artillery system did not cause any complaints. It was also found that the self-propelled guns had better accuracy (due to the greater rigidity of the mount), but it was not possible to fire on the move because of the strong "bumpiness" inside the crew compartment, even at the lowest speed. Further tests were discontinued due to the absence of ammunition.

Based on the available results in 1932, an improved design of the SU-1 was prepared, but at that time, the T-26-4 “arttanka” and the AT-1 self-propelled unit with the best design qualities were already preferred. As for the project of the German company Daimler-Benz, NTK UMM refused in view of its implementation at once for two reasons. First, the German development was strongly delayed in time and was introduced only in 1933. Secondly, the cost of developing the German ACS was much higher than planned.

However, in 1936, they returned to this project again. After radical processing and use of the undercarriage from the medium tank Pz.Kpfw.III, it was possible to get one of the best ACS of the Second World War - the StuG III.