SU-3 / SU-76 / SU-76K / TPK-27

The designators SU-3, SU-76 and SU-76K are at times applied more or less interchangebly, but in fact seem to reference two kindred but distinct vehicles. The SU-3 and SU-76K designators seem to apply to a T-27 Tankette with a 76mm Kurchevsky recoilless rifle [hence the K in SU-76K], while the SU-76 references a conventional 76mm gun on a T-27.

The tankette ["wedge"] in the 1920-30s was considered quite a logical means of conducting reconnaissance. The basis was, as was fashionable at the time, the English wedge "Cardin-Loyd" Mk VI. In 1929, a state commission under the leadership of I. A. Khalepsky purchased a sample and documentation. T-27s were used in reconnaissance units of combined arms and tank formations, were in service with the airborne brigades, where large-scale experiments were conducted with them to parachute and parachute landing.

Attempts were made to install even more powerful weapons on the T-27, including the Hotchkiss 37-mm cannon and the 76.2-mm cannon, but they had to be abandoned because the chassis could not withstand the increased mass of the vehicle. Moreover, tests had shown that a light (less than 3 tons) wedge just lost stability when firing guns of this caliber.

In 1935, the air transportation of T-27 tankette suspended from heavy TB-3 bombers was tested. The device with which the suspension was carried out was developed by the inventor A. F. Kravtsev. With the help of this device, the T-27 was not only suspended from aircraft, but also dropped from low altitude to the ground.

In 1933, light self-propelled artillery mounts, armed with a 76-mm Kurchevsky dynamo-reactive cannon, were created on the basis of this tankette, but did not go into the series, as was also the case with all the “brilliant” works of Kurchevsky. According to the documents, this self-propelled guns passed as a “small artillery self-propelled gun SU-3” or T-27K , although a number of sources include the designation SU-76K (self-propelled gun with a 76 mm Kurchevsky gun). The prototype self-propelled gun built in 1933 differed from the serial wedge solely in the presence of a strongly protruding barrel and gun nozzle.

In December 1931, the UMM RKKA approved a technical task for the small SU-3 - the installation of a 76-mm dynamo-active (recoilless) K gun designed by LV Kurchevsky on a T-27 wedge. This self-propelled gun was intended for action as part of reconnaissance units and escort cavalry. SU-3 was developed in 1933 at plant number 7 and in the same year made its prototype.

During 1933-1934, the special design bureau of the Krasny Putilovets plant designed a self-propelled unit with a 76-mm KT gun of the year based on the T-27 tankette. The gun was mounted on one wedge, and the ammunition and gun crew was transported to another. The crew consisted of two people. The main weapon was a dynamo (recoilless) K gun designed by LV. Kurchevsky, which was installed instead of the standard 7.62-mm machine gun DT at the right side of the machine. There was an automatic reloading mechanism. All parts of the gun, except the nozzle and the tray, were protected by armor 6 and 9 mm thick. The power plant, transmission, chassis and electrical equipment remained unchanged. The range of the SU-76K on the highway reached 110 km. If necessary, a quick transfer self-propelled unit could be transported behind the car on a trolley with pneumatic tires.

The SAU with a 76-mm recoilless Kurchevsky gun was designed and manufactured in an installation with all parts except the nozzle and the tray were covered with armor. The Kurchevsky gun was installed instead of the regular DT machine gun at the starboard side of the vehicle and according to some sources had a horizontal pointing angle of 5°, and a vertical one, from -1° to + 5°. Other sources report an elevation angles of the barrel of 0.5 - 15 degrees, Horizontal fire - 55 degrees. from the starboard side and 60 degrees. on the left, the mass of the projectile was 6.23 kg, and its initial velocity was 341 m/s [some sources report the initial velocity of the projectile was 300 m/s]. Ammunition - 30 shots. The gun was equipped with an automatic reloading mechanism. All its parts, except for the nozzle and the tray, were protected by 6- and 9-mm armor. The engine, transmission and chassis of the installation remained unchanged (compared with the T-27).

For firing from a cannon, unitary shots were used with shrapnel shell, fragmentation and armor-piercing grenades. The longest range of the fragmentation grenade was 7000 m. In addition, the military was attracted by the small weight of the gun, which did not exceed 180 kg.

On March 25 and 26, 1933, several self-propelled artillery systems with Kurchevsky guns were simultaneously tried at the MKUKS training ground in Kuntsevo: the T-27 wedge, the T-26 tank, the BAI armored car and the three-axle Ford vehicle. The chairman of the testing committee was the head of the NIABCP Shtagin. From OKB GAU in trials participated Kurchevsky, from NTK GAU - Krause, from NTK UMM - Saks, Saprykin and Skvirsky, from the 2nd branch of the 2nd management - Fokin, from NTU UMM - Azbukin.

From April 15 to April 25, 1933, the Su-3 was tested at the VAMM test site named after Stalin in Kuntsevo. During the tests, a rupture of the barrel occurred, and the engineer A.Y.Neyland died as a result of the explosion. After repair at plant number 8 in Podlipki SU-3 was shown to the authorities at the chemical site in Kuzminki.

SU-76K was recognized suitable for extensive testing at the NIAP under the UMM program and the GAU with the elimination of the identified deficiencies. These tests took place from July 23 to August 29, 1933. 575 shots were fired from a cannon, and the total mileage of the car reached 100 km. The rate of fire was 6-7 shots / min. During the tests, protracted shots and spitting were recorded (about 5%) - shells falling 3-4 meters otdula. Accuracy at distances of up to 400–600 m was considered acceptable, and at large distances, unsatisfactory.

It was was admitted to the military, but the latter gave negative results, as the gun had poor ballistic qualities, was unsafe to handle. The gun strongly unmasked itself during firing, a it could burn a nearby Red Army soldier to death (dynamo-cannon cannons throw a stream of hot gases backwards, eliminating recoil). In addition, in the tiny body of the wedge was not enough room to store ammunition to the gun. At the proving ground tests, the SU-3 proved to be quite worthy, but the military revealed many shortcomings, the most significant of which were the poor ballistic characteristics of the gun and the insecurity of its operation. When fired from the nozzle, a powerful jet of gases escaped, and a strong sound and a cloud of dust unmasked the installation. As a result, the project also had to be abandoned.

A variant with a 45 mm cannon, created on the basis of the SU-3, was also rejected. The gun on this self-propelled gun was installed in the rear of the hull and was covered with armored shield. As in the case of the KT-27, the gun crew and the gun itself were transported on different wedges, which did not suit the military at all. As the last measure to increase the firepower of the wedge, an experiment on the installation of unguided rockets can be noted. Two RS-132s were mounted on the sides of the T-27 hull on special guides, and missiles were launched from the fighting compartment. Such a system was not developed in view of the low aiming range.