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ISU-122S

In later models ISU-122 the A-19 gun was modified to have a semi-automatic breech block. This gun was designated D-25S, and the vehicle mounting it ISU-122S. The modification increased rate of fire from 1.5 rounds/minute to 3 rounds/minute. The ISU-122S variant is recognizable by its ball-shaped gun mantlet and double-baffle muzzle brake. This heavy assault gun, built on the basis of the IS tank, was effective against German heavy tanks as well as fortifications. The prototype was built at the Chelyabinsk Kirov Plant in April 1944. The vehicle entered service in August of that year, and a total of 675 vehicles were manufactured in 1944 and 1945.

The ACS ISU-122S ("Object 249", ISU-122-2) was created in April 1944 and was a modernized version of the self-propelled installation of the ISU-122, differing from it by the installation of the 122 mm cannon D-25C arr. 1944 with a wedge semi-automatic shutter and a muzzle brake, as well as a 12.7-mm anti-aircraft machine gun DShK. The height of the line of fire was 1795 mm. The crew of the car consisted of five people, its placement was similar to the placement of the crew in the installation of ISU-122 (ISU-152). In June, the installation was running and artillery trials. It was adopted on August 22; mass production began in August 1944 at ChKZ.

From August 1944 to September 1945, a parallel release of the ISU-122 with the A-19 cannon and the ISU-122C with the D-25C cannon was organized, due to the lack of D-25C cannons. Until June 1, 1945, 475 ISU-122S self-propelled guns were manufactured, which were used in battles in the final period of the Great Patriotic War. In total, 675 cars were manufactured.

The D-25S gun was no different from the D-25 gun installed in the IS-2 tank, with the exception of the installation of a new recoil brake and a modified modified semi-automatic wedge gate.

The length of the barrel was 48 calibers. The balancing of the oscillating part of the gun was carried out using a spring balancing mechanism. The shutter had a horizontal displacement of the wedge and a more compact and simple semi-automatic rolling type. The disadvantage of the semiautomatic of the rolling type was its shock effect, as a result of which there were great forces acting on the shutter parts. The horizontal movement of the wedge reduced the effort required for opening and closing it, improved the loading conditions and made it possible to slightly increase the layout density of the swinging part. Therefore, the release and installation in the self-propelled gun installation D-25C began without testing a prototype. The use of this gun slightly increased the combat rate of fire - up to 6 shots / min.,

Vertical pickup angles ranged from - 3 to + 20 °, horizontally - in a sector of 10 ° (7 ° to the right and 3 ° to the left). When firing direct fire, a TSH-17 telescopic articulated sight (10T-17) was used, from closed firing positions a panoramic sight with a semi-independent aiming line (Hertz panorama). The pickup drives remained unchanged compared to the drives of the self-propelled ISU-122 installation. The trigger mechanism of the instrument was lowered by pressing the mechanical lowering lever (on the left shield of the fence) or by the electric trigger lever (on the handle of the lifting mechanism flywheel). Direct firing range was 5000 m, the greatest - up to 15 000 m.

The ammunition consisted of 30 shots of a separate cartridge loading with an armor-piercing-tracer: a sharp-headed projectile and a projectile with a ballistic tip (BR-471 and BR-471B) with an MD-8 fuse, as well as high-explosive cannon grenades: a full-cornered long-sleeved pattern and a short pattern and a short pattern and a short pattern and a short pattern and a short pattern and a short pattern and a short pattern and a long pattern and a short pattern and a short pattern and a short pattern and a short pattern and a short pattern and a short pattern and a short pattern and a short pattern and a short pattern and a short pattern and a short pattern and a short pattern and a short pattern and a short pattern and a short pattern and a short distance pattern and a short pattern and a long rifle piece and a short-armored grenade: screwed head (OF-471 and OF-471N) with fuses RGM and D-1.

The charges are full and the third, which differed from each other by the weight of gunpowder. The full charge was used for firing armor-piercing tracer shells and high-explosive fragmentation grenades. The third charge was used only for firing high-explosive fragmentation grenades. The initial velocity of the armor-piercing-tracer projectile with a mass of 25 kg was 781 m / s. Ammunition for the DShK anti-aircraft 12.7-mm machine gun mounted in the turret on the roof of the armor cabin on the rotary base of the right hatch, amounted to 250 rounds. Additionally, in the fighting compartment fit two 7.62-mm submachine gun PPSh (PPS) with ammunition 497 rounds (7 disks) and 25 F-1 hand grenades.

The armor protection was counter-equipped, it was kept at the level of the armor protection of the self-propelled unit IZU-122. The power plant, transmission, chassis and electrical equipment of the machine were borrowed from the self-propelled installation of the ISU-152.

The use of the D-25S gun restored the superiority lost over time to the enemy in artillery armament. It had higher characteristics than the German 75- and 88-mm cannons, and provided penetration of armor of enemy tanks at ranges up to 2500 m. The total length of the vehicle (9950 mm) was 100 mm greater than the length of the self-propelled ISU-122 installation and therefore more limited its maneuverability.