SU-76 [T-27] self-propelled regimental gun
The idea to equip the "wedge" tankette with cannon weapons did not belong to Soviet specialists, but it was in the USSR that this topic was most widely used. Immediately after the start of serial production of T-27, the leading engineer of plant No. 37 K. Sirken, who had previously participated in adapting the English version to the requirements of the Red Army, proposed to equip this machine with a 37 mm Hotchkiss short-barreled gun. This tool was widely known due to its compactness and good performance. The aiming range of the Hotchkiss was 300 meters, with a maximum of 2000 meters. The initial velocity of the projectile was 442 m/s.
Although it was not planned to make big changes, the wedge body had to be modified a bit. The gun was mounted on a carriage on the right side in a superstructure extended forward. A standard 7.62 mm DT machine gun was mounted above it. Since the internal volume of the wedge did not allow to put shells there, the ammunition for the gun was transported on a special caterpillar trailer. The undercarriage of the T-27 had also undergone changes - instead of the track supporting the caterpillar, two metal rollers were installed from each side. The rest of the cannon wedge did not differ from the original.
When assembling the hull, the armor plates were still fastened with rivets, and the reservation was from 4 to 10 mm (forehead, side and upper back sheet - 10 mm, lower back sheet and dome - 6 mm, lower case sheet - 4 mm). Modifications of Sirken did not find proper support from the military for obvious reasons. To deliver ammunition crew would have to leave the vehicle, which was far from always possible in combat conditions.
The next attempt could turn out to be more successful; in fact, the very principle of the “diversity” of guns and ammunition ruined everything. On August 5, 1933, the Revolutionary Military Council of the USSR approved the "Red Army Artillery System for the Second Five-Year Plan." As part of this program, in 1934, the T-27 chassis developed a battalion 45-mm universal self-propelled gun. In the same year, in the special design bureau of the Krasny Putilovets plant, under the leadership of I. Makhanov, they designed a self-propelled unit SU-76. By analogy with the 45-mm installation, the shield-covered 76-mm regimental gun of the 1927 model was installed in the rear part of the T-27 chassis. When shooting, to give the car stability, there were two reclining counter-stops. In order to reduce the height of the line of fire to 1250 mm, the layout of the engine compartment of the car was changed - the fuel tank and the cooling system radiator were moved. The angle of horizontal guidance was possible in the sector of 36° without turning the machine, because the gun was borrowed along with the upper machine. The angle of vertical guidance was from -3° to + 35°.
Because of the small size of the machine, neither a full gun crew or ammunition could be placed in it. Therefore, the SU-76 was attached to another machine, developed on the basis of tanketki T-27 for the transport of calculation and ammunition. However, this was the main disadvantage of the self-propeller. The division of the combat unit "gun + calculation + ammunition" into two cars could lead to a detachment in combat (for example, due to a breakdown of the engine or running gear) of the calculation with ammunition from the gun. Three prototypes of this SU-76 were made in 1935.
In 1933, on the T-27, the forces of the engineers of the Krasny Putilovets factory created a new artillery system, which, in terms of tactics, was more in line with self-propelled guns. This system consisted of two wedges: on one of them (“cartridges”) the crew of a gun of 2 people and an ammunition of 50 shells was carried, on the second a 76.2mm KT-27 regiment gun was installed with the driver’s place remaining and ammunition for 8 shots. Directly on the "artillery" T-27 it was necessary to almost completely cut off the superstructure, covering the gun with folding shields. The height of the wedge was reduced, amounting to 1250 mm on the line of fire. In this regard, the fuel tank and the engine cooling radiator were transferred to the stern, while simplifying the power supply circuit. The gun had angles of vertical guidance from -3° to +35° and horizontal +\- 18°.
An order was received from the Red Army for the construction of several prototypes, three of which were delivered by the beginning of 1934. During the tests, the self-propelled guns could not show the required characteristics. When firing, there was a strong recoil, so it was not recommended to fire without installing the hinged stops. Some of the self-propelled guns were not equipped with side shields, and when driving off-road, the motor of a heavy platform wedge was very hot and out of order. In this form, the artillery system on the T-27 chassis could not be put into service and work to improve it was stopped.
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