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SU-76I / SU-S-1

The SU-76 (Samokhodnaya Ustanovka 76) was a Soviet self-propelled gun used during the Great Patriotic War. The unrelated SU-76I (1943, where "I" means "foreign") was based on the German Panzer III and StuG III chassis, armed with a ZiS-5 76.2 mm gun. Among the trophies of the Red Army, there were a significant number of serviceable tanks PzKpfw III and PzKpfw IV. Therefore, in 1942 it was decided to develop on their base self-propelled artillery installations armed with Soviet 76.2-mm cannon ZIS-3.

In January-February 1943, mass transmission accidents adopted by the SU-76 (SU-12) began to occur . The cause of these accidents was the parallel installation of two twin engines operating on a common shaft, which led to the emergence of resonant torsional vibrations. The defect was considered structural, and its elimination required a lot of time. Thus, in February 1943, most of the SU-76 (SU-12) required repair and could not be used for combat. The Red Army was deprived of the most needed 76-mm self-propelled divisional guns. An urgent need was to find a temporary solution for the manufacture of self-propelled 76-mm guns for the summer campaign of 1943.

When the constructive defect of SU-76 (SU-12) was identified, GoKO required finding an urgent decision on fulfilment of the volume of manufacturing of SP gun for support to summer battles in 1943. The most simple was the offer of A.Kashtanov, who wanted to make a SP guns on the chassis of captured tanks. For a basis a design of self-propelled 122-mm howitzer SG-122 was taken, because SG-122 already was tested on Gorochovetski proving ground.

The design of SG-122 was changed. Instead of the M-30 howitzer, the new battle vehicle was armed a special cannon for self-propelled guns S-1, which was altered from a tank gun F-34. On March 6 1943 experimental sample of new SP gun began a production tests. The serial manufacture of SP gun SU-S-1 (SU-76I) proceeded on a factory 37 since May 1 to October 1 1943. They assembled total 201 machines.

The experience in creating the self - propelled guns of the SG-122 (A) on the basis of the captured Arthturm was not in vain - it was needed at that moment when the self-propelled guns of the SU-76 , which our command was so counting on, and which the soldiers and commanders of the infantry divisions were waiting for, began in mass order fails due to a design error of its chief designer Semen Ginzburg. Sending the latter to the front could not compensate for the loss of time it took to rework the SU-76 into the SU-76 M. Therefore, as a temporary measure, it was proposed to produce self-propelled guns based on captured chassis from German tanks Pz.III and assault rifles created on its base. guns StuG III Artsturm. After successful operations at Stalingrad, in the Middle and Upper Don such a huge number of cars accumulated in the warehouses of captured property.

The decision on the preparation of mass production assault 76-mm The ACS support for the trophy chassis was taken on February 3, 1943. The design team of Kashtanov was transferred to Sverdlovsk, into the territory of the evacuated plant No. 37, and by the order of the NKTP was transformed into the design bureau and began the revision of the SG-122 project. There was little time, since the prototypeACSshould have been ready by March 1. Therefore, the drawings of many nodes were already made backdating, measuring the prototype. In contrast to the previously manufactured self-propelled howitzers, cutting in the newACSreceived inclined sides, which increased their strength. Initially it was planned to install a76.2-mm ZIS-3 cannon in the combat compartment of theSAU on the machine, reinforced to the floor, but such an installation did not provide reliable protection of the gun embrasure from bullets and shrapnel, since during lifting and turning the gun in the shield there were always cracks. But this problem was resolved by installing a special self-propelled 76.2 mm S-1 gun instead of the 76-mm divisional gun. This gun was designed on the basis of the design of an F-34 tank gun and was very cheap. It was developed for light experimental self - propelled guns of the GAZ plant. From the F-34, the new gun was distinguished by the presence of a cardan frame, which allowed it to be installed directly into the frontal hull sheet and freed up the useful volume in the combat compartment.

The installation was carried out according to the layout scheme with the front arrangement of the combined transmission and control compartments, and the aft engine compartment. The fighting compartment was located in the middle part of the corps, above which was placed the armored wheelhouse with installed weapons. Department of management and transmission, which housed the driver, directly connected with the fighting compartment.

The engine compartment was separated from the fighting partition, which had a hatch for access to the engine, closed the door. In the fighting compartment to the right of the gun was placed the commander, to the left in front - the gunner, behind him on the casing of the transmission shaft - loader. The landing and exit of the crew were carried out through the hatch, closed by double-winged armor covers and located in the stern sheet and the cabin roof. To observe the battlefield and driving the machine, the driver in the front and left side hull sheets had access hatches with triplex and armor valves. The rest of the crew observed the battlefield using the PTK command panorama and viewing slots located in the frontal and side sheets of the armor-house, equipped with armor valves.

The angles of vertical guidance of the gun ranged from -5 to + 15 °, on the horizon - in the sector ± 10 °. The TMFD-7 telescopic sight and the ZIS-3 76.2 mm cannon were used for shooting. The rate of fire was 5-6 shots / min. The unit’s ammunition consisted of 96 unitary shots with a steel high-explosive long-range grenade (OF-350, O-350A, F-354), an armor-piercing tracer shell (BR-350A, BR-350B, BR-350SP), a cumulative projectile (BP -353A), piercing armor-piercing tracer shells (BR-354P), bullet shrapnel (W-354, W-354T and W-354G) and canister (S-350). Shots were placed: 48 pcs. - in the right rear corner of the cabin on the horizontal rack, 38 pcs. - in vertical uprights along the left side and 10 pcs. - in a vertical rack along the starboard side.

The first self-propelled guns had a rather “spartan” look. Their conning tower was welded from 35 mm thick armor plates in the frontal part and 25 mm or 15 mm in the sides and stern. The armor protection provided protection for the crew and the internal equipment against the fire of large-caliber machine guns and shell fragments. The roof of the cabin was originally cut out of a single sheet and fastened with bolts. This facilitated access to the combat compartments of the self-propelled guns for repairs, but after the battles of the summer of 1943, many of the self-propelled guns had the roof removed to improve habitation.

In the sides of the hull in the combat compartment area, inside the caterpillar bypass (when using the base of the T-III tank) there were two escape hatches closed by armored covers. In the rear hull sheet for the crank of the inertial starter, a special hatch was made, closed by an armored valve. The cabin had the shape of a truncated pyramid with rational tilt angles of armor plates and was attached to the body of the vehicle with the help of bolts. The joint of the armored cabin and the hull of the vehicle was reinforced with weld-on armor plates 10 mm thick. For firing from a PPSh submachine gun in the left and right sides, as well as in the left wing of the aft hatch of the cabin, openings were made that were closed with armored gates. In addition, there was also a round hole in the frontal heading for this purpose, which was closed by an armored stopper. On a part of self-propelled units (about 20 cars) - commander vehicles from August 1943, on the roof of the wheelhouse on the right, a commander's turret was installed with a special access hatch, the design of which was borrowed from the German T-III tank. On these machines, an enhanced radio station was installed, as a result of which the ammunition for the gun was reduced.

In the engine compartment there was a four-stroke carburetor twelve-cylinder V-engine "Maybach" HL120TRM liquid cooling capacity of 300 hp (221 kW) with two Solex carburetors. The engine was started using a Bosch type electric starter of the BNG type with a capacity of 4 hp. (2.9 kW) or manually - using an inertial starter. The ignition system used magneto "Bosch" type 1012L14 or domestic production of BSM-12Sh. For access to the engine compartment in its roof were made four hatches, closed with armored covers.

Depending on the modification of the used chassis of the German trophy tank Pz.III on the SU-76I Two types of Maybach gearbox and main friction clutch were used: the six-speed manual gearbox ZF Athos SSG77 (six forward gears and one reverse gear) and the dry three-disk main clutch with mechanical control or the mechanical gearless ten gearbox Maybach Variorx "SRG 328145 with a synchronizing device and semi-automatic pneumohydraulic pre-selector control (ten forward gears and four gears when reversing) and two-disc ch Oil friction clutch. When using a six-speed gearbox, the main clutch was mounted on the engine in the engine compartment. The transmission of torque from the engine to the gearbox was carried out using a transmission shaft.

In the department of control and transmission, a gearbox was installed (using a ten-speed gearbox) and the main friction clutch assembled with it, single-stage planetary rotation mechanisms with supporting brakes, transverse drive shafts, control brakes and actuators for controlling the propulsion system. When using a six-speed gearbox, two types of brake control could be used: mechanical and hydraulic. Outside in the front of the hull sides in the armored crankcases housed the onboard gearboxes.

The suspension system included an individual torsion suspension, rubber limit stops for all support rollers, and hydraulic shock absorbers on the extreme support rollers. The crawler propulsion unit consisted of two front-wheel drive wheels with removable gear rims, twelve two-pitched support and six dual-pitched supporting rollers with external cushioning, two guide wheels with caterpillar tensioning mechanisms, and two tracks with a track width of 380 mm.

Electrical equipment SU- 76I was performed by a single-wire circuit. The voltage of the on-board network was 12 V. Two electric batteries with a capacity of 128 or 144 Ah and a Bosch type generator 600 kW with a 600 W relay were used as power sources. Since the radio stations were in short supply in early 1943, they were installed on every third car, especially since most of the SAU came in training units. But since mid-May, almost every SU-76I was supplied with radio stations of the 9-P type.(C-1). The trials were held in the vicinity of Sverdlovsk by mileage along roads and snow virgin lands with a jammed and disengaged instrument. Despite the severe weather conditions (during the day - the thaw, and at night - the frost, which reached minus 35 degrees), the car performed well, and on March 20, 1943, the car was recommended for use under the SU C-1, SU-76 (C-1) or SU-76I ("Foreign"). The first five serial SAUApril 3, 1943 were sent to the educational self-propelled artillery regiment stationed in the suburbs of Sverdlovsk. During the month of service, the cars “dashed off” from 500 to 720 km and assisted in the training of more than 100 future gunners. Reviews about the car were good, and only the difficulty of starting the engine in the cold was noted by all the technicians as a “lack of first importance”.

Meanwhile, according to the refined drawings, the plant began manufacturing a “front-line” series of 20 self-propelled guns , which for the most part also fell into the training units. Only from May 1943, the SU-76 (S-1) began to enter the army. At the end of July 1943, according to the experience of using SU-76Ion the Kursk Bulge, an armored reflective shield was installed on the swinging armor of the gun, the purpose of which was to prevent the gun from jamming by small pieces and bullets. At the same time, in order to increase the reserve, self-propelled guns began to be equipped with two external fuel tanks, which were installed along the stern on the easily resettable brackets. Cruising the car on the highway using only the main fuel tank reached 180 km, and the capacity of the main fuel tank was 320 liters. External tanks also contained another 120 liters of fuel.

Initially , captured PzKpfw III was used as commander vehicles in self-propelled artillery regiments (SAP) armed with SU-76Is . In August, it was decided to manufacture also special commanding self-propelled guns , which were equipped with a commander's turret from PzKpfw III and a radio station of increased power with reduced ammunition.

The last SU-76Is left the factory’s workshops at the end of November 1943. By this time, the shortcomings of the domestic SU-76 were eliminated and the self-propelled guns in the required quantity were shipped to the front by two NKTP enterprises (Plant No. 38 in Kirov and GAZ in Gorky). Soviet self-propelled guns were cheaper and lighter than SU-76Iand besides, there were no problems with their supply of spare parts. In total, during the mass production of the SU-76I, at plant No. 37, 201 self-propelled guns were produced (including 20 “commanding”).

Baptism of fire units equipped with SU-76I received at the Kursk Bulge. It is known that by the beginning of July 1943, the 13th Army of the Central Front had at its disposal 16 SU-76s on the trophy chassis. And during the defensive battles, eight such machines were lost (three were burned). The Voronezh Front also had a certain amount of SU-76I , but in the front report at the beginning of the battles, only the total number of all ACS with a 76-mm cannon (33 pieces) was given.

It is also known that during the attack on the Eagle, the Central Front was strengthened by two self-propelled artillery regiments, one of which also had vehicles on the trophy chassis (16 SU-76I and one PzKpfw III tank).

It is reliably known that on August 2, 1943, the 1902th SAP, consisting of 15 Su-76Is , arrived in the 5th Guards Army . Until August 14, the regiment was not introduced into the battle, but was engaged in repairing the ACSand waited for replenishment by motor transport (initially the number of cars in the SAP was 10% of the regular number). At the same time, five SU-122s arrived at the recruiting of the regiment. From August 14 to August 31, the regiment participated in five battles (on average, 2-3 battles more than any other regiment of the army). During this period, self-propelled guns destroyed two tanks, nine guns, 12 machine guns and up to 250 soldiers and officers. According to the report of the regiment commander of September 1, “all vehicles in previous battles are damaged. Separate cars were restored several times, the whole materiel SU-76 (based on PzKpfw III) is worn out and is in poor condition. The regiment was constantly understaffed, the training of personnel was satisfactory. ”

In September 1943, the regiment took part in 14 battles in which was introduced at the same time from two to seven self-propelled guns . The fire of self-propelled units provided substantial assistance to the infantry in repelling enemy attacks.

The most productive battles took place during September 20-23, 1943 during the pursuit of the departing enemy, when a group of six SU-76Is destroyed three enemy tanks.