In the initial period of the war, several dozen 75-mm Sturmgeschütz III (StuG III) self-propelled guns were among the trophies of the Red Army. In the absence of their own self-propelled guns, captured StuG IIIs were actively used in the Red Army under the designation SU-75. German "artillery attacks" had good combat and service-operational characteristics, had good protection in the frontal projection, were equipped with excellent optics and a completely satisfactory weapon.
The first report of the use of the StuG III by Soviet troops dates back to July 1941. Then the Red Army during the Kiev defensive operation managed to capture two serviceable self-propelled guns.
Subsequently, some of the captured "artillery attacks" requiring factory repairs were converted into the SU-76I self-propelled guns, and serviceable vehicles were used in their original form. Some SPGs of the StuG III Ausf. F and StuG III Ausf. G, armed with long-barreled 75-mm guns and protected by 80-mm frontal armor, were operated in the Red Army until the end of the war as tank destroyers.
By the middle of 1942, the Soviet command had accumulated some experience in the use of captured self-propelled guns and had an idea of what an "artillery assault" should be, intended for firing at visually observed targets. Experts came to the conclusion that high-explosive fragmentation 75-76, 2-mm shells are suitable for providing fire support to infantry, they have a good fragmentation effect on the enemy's undiscovered manpower and can be effectively used to destroy light field fortifications. But against capital fortifications and brick buildings turned into permanent firing points, self-propelled guns were required, equipped with larger caliber guns. Compared to the 76, 2-mm projectile, the howitzer 122-mm high-explosive fragmentation projectile had a significantly greater destructive effect. The 122-mm projectile, which weighed 21.76 kg, contained 3.67 kg of explosives against 6.2 kg of a "three-inch" projectile with 710 g of explosive. One shot from a 122-mm gun could achieve more than a few shots from a three-inch gun.
Self-propelled artillery unit SG-122
Taking into account the fact that in the Soviet warehouses of captured armored vehicles there were a significant number of captured StuG III self-propelled guns, at the first stage it was decided to create an self-propelled gun based on them, armed with a 122-mm M-30 howitzer.
However, to accommodate the 122 mm M-30 howitzer, the StuG III wheelhouse was too cramped and a new, larger wheelhouse had to be redesigned. The Soviet-made fighting compartment, which housed 4 crew members, became significantly higher, its frontal part had anti-cannon armor. The thickness of the frontal armor of the cabin is 45 mm, the sides are 35 mm, the stern is 25 mm, the roof is 20 mm. For the conversion, the StuG III Ausf. C or Ausf. D with 50 mm frontal hull armor, side armor thickness was 30 mm. Thus, the security of the self-propelled gun in the frontal projection approximately corresponded to the T-34 medium tank.
The self-propelled gun received the designation SG-122, sometimes there is also SG-122A ("Artshturm"). Serial production of self-propelled guns on the StuG III chassis began in the late autumn of 1942 at the non-evacuated facilities of the Mytishchi Freight Car Building Plant No. 592. In the period from October 1942 to January 1943, 21 self-propelled guns were handed over to military acceptance.
Part of the SG-122 was sent to self-propelled artillery training centers, one machine was intended for testing at the Gorokhovets training ground. In February 1943, the 1435th self-propelled artillery regiment, which had 9 SU-76s and 12 SG-122s, was transferred to the 9th Panzer Corps of the 10th Army of the Western Front. There is little information about the combat use of the SG-122. It is known that in the period from March 6 to March 15, the 1435th SAP, participating in battles, lost all its materiel from enemy fire and breakdowns and was sent for reorganization. During the battles, about 400 76, 2-mm and more than 700 122-mm shells were used up. The actions of the 1435th SAP contributed to the capture of the villages of Nizhnyaya Akimovka, Verkhnyaya Akimovka and Yasenok. At the same time, in addition to firing points and anti-tank guns, several enemy tanks were destroyed.
Apparently, the combat debut of the SG-122A was not very successful. In addition to poor training of personnel, the effectiveness of self-propelled guns was negatively affected by the lack of good sights and observation devices. Due to poor ventilation during firing, there was a strong gas contamination of the conning tower. Due to the tightness of the working conditions for the commander, two gunners and the loader were difficult. Experts also noted the excessive congestion of the front rollers, which affected the reliability of the chassis.
To date, not a single original SG-122 SPG has survived. The copy installed in Verkhnyaya Pyshma is a model.
Self-propelled artillery unit SU-122
In connection with the revealed shortcomings of the SG-122 and the limited number of StuG III chassis, the 122-mm self-propelled artillery unit was decided to be built on the basis of the T-34 tank. The SU-122 self-propelled gun did not appear out of nowhere. At the end of 1941, in order to increase the production of tanks, a reckless T-34 project was developed with a 76, 2-mm cannon installed in the wheelhouse. Due to the abandonment of a rotating turret, such a tank should have been easier to manufacture and have thicker armor in the frontal projection. Later, these developments were used to create a 122-mm self-propelled gun.
In terms of the level of security, the SU-122 practically did not differ from the T-34. The crew consisted of 5 people. The self-propelled gun was armed with a "self-propelled" modification of the 122-mm howitzer mod. 1938 - М-30С, while maintaining a number of features of the towed gun. So, the placement of the controls for the aiming mechanisms on opposite sides of the barrel required the presence of two gunners in the crew, which, of course, did not add free space inside the fighting compartment. The range of elevation angles was from −3 ° to + 25 °, the horizontal firing sector was ± 10 °. The maximum firing range is 8000 meters. Combat rate of fire - up to 2 rds / min. Ammunition from 32 to 40 rounds of separate-case loading, depending on the series of release. These were mainly high-explosive fragmentation shells.
Field tests of the SU-122 prototype were completed in December 1942. Until the end of 1942, 25 self-propelled units were manufactured. At the end of January 1943, the first two self-propelled artillery regiments of mixed composition arrived at the front near Leningrad. The SAP consisted of 4 batteries of light self-propelled guns SU-76 (17 vehicles) and two batteries SU-122 (8 vehicles). In March 1943, two more self-propelled artillery regiments were formed and manned. These regiments were placed at the disposal of the commanders of the armies and fronts and were used during offensive operations. Subsequently, a separate formation of regiments began to be carried out, equipped with 76, 2- and 122-mm self-propelled guns. According to the staff, the SAP on the SU-122 had 16 self-propelled guns (4 batteries) and one commander's T-34.
In units of the active army, the SU-122 was met better than the SU-76. The self-propelled gun, armed with a powerful 122-mm howitzer, had higher protection and proved to be more reliable in operation.
In the course of hostilities, the most successful application was the use of the SU-122 to support the advancing infantry and tanks while being behind them at a distance of 400-600 meters. In the course of breaking through the enemy defense, self-propelled guns with the fire of their guns carried out the suppression of enemy firing points, destroyed obstacles and barriers, and also repelled counterattacks.
The anti-tank capabilities of the SU-122 turned out to be low. Even the presence in the ammunition load of the BP-460A cumulative projectile with normal armor penetration up to 160 mm did not make it possible to fight with tanks on an equal footing. A cumulative projectile weighing 13.4 kg had an initial velocity of 335 m / s, and therefore the effective range of a direct shot was a little more than 300 m. In addition, firing at fast-moving targets was a very difficult task and required well-coordinated crew work. Three people took part in pointing the gun at the target. The driver carried out approximate aiming of the tracks using the simplest sighting device in the form of two plates. Further, the gunners entered the work, servicing the mechanisms of vertical and horizontal guidance. With a low rate of fire of a howitzer with a separate-sleeve loading, an enemy tank could respond with 2-3 shots for each aimed shot of the SU-122. The 45-mm frontal armor of the Soviet self-propelled gun was easily penetrated by 75- and 88-mm armor-piercing shells, and direct collisions of the SU-122 with German tanks were contraindicated for it. This is confirmed by the experience of combat operations: in those cases when the SU-122 participated in frontal attacks along with line tanks, they invariably suffered heavy losses.
At the same time, with the correct tactics of use, the good performance of 122-mm high-explosive fragmentation shells against enemy armored vehicles was repeatedly noted. According to the reports of the German tankers who participated in the Battle of Kursk, they repeatedly recorded cases of serious damage to heavy tanks Pz. VI Tiger as a result of shelling with 122 mm howitzer shells.
Production of the SU-122 was completed in August 1943. Military representatives received 636 vehicles. SU-122s actively participated in the battles of the second half of 1943 and the first months of 1944. As their numbers decreased due to the relatively small number in the troops, the termination of serial production and various losses, they were removed from the SAP, which were re-equipped with SU-76M and SU-85. Already in April 1944, SU-122s became rare vehicles in the Soviet armored vehicle fleet, and only a few self-propelled guns of this type survived until the end of the war.
The termination of serial production of the SU-122 is primarily due to the fact that this ACS was armed with a 122-mm howitzer, which was not very well suited for a self-propelled gun, primarily intended for firing at visually observed targets. The M-30 divisional 122-mm howitzer was a very successful artillery system, still in service in a number of countries. But in the case of arming her self-propelled guns, created on the T-34 chassis, a number of negative points emerged. As already mentioned, the range of a direct shot from the M-30S adapted for the ACS was relatively small, and the SU-122 did not fire from closed positions, when all the advantages of the howitzer could be manifested. Due to the design features of the 122-mm howitzer, two gunners had to be added to the self-propelled gun crew. The gun took up too much space in the fighting compartment, creating significant inconvenience to the crew. The large forward reach of the recoil devices and their booking made it difficult for the driver to see from the driver's seat and did not allow a full-fledged hatch to be placed on the front plate. In addition, the 122 mm howitzer for the undercarriage of the T-34 tank was heavy enough, which, combined with the forward movement of the gun, overloaded the front rollers.
Self-propelled artillery installation ISU-122
In this situation, by analogy with the SU-152, it was logical to create a heavy self-propelled gun on the chassis of the KV-1S tank, armed with a 122 mm A-19 cannon. However, in real history this did not happen, and the creation of the ISU-122 self-propelled gun on the chassis of the IS-2 heavy tank was largely due to the shortage of 152-mm ML-20S guns. In addition, the need for well-protected tank destroyers was revealed, which, in terms of effective firing range, would have surpassed German heavy tanks equipped with 88 mm cannons. Since our troops, which went over to offensive operations, were in dire need of heavy self-propelled guns, it was decided to use the 122-mm A-19 guns, which were in abundance in the artillery depots. In this place, within the framework of the story about Soviet 122-mm self-propelled guns, we will move away from the chronology of the development of domestic self-propelled guns and take a closer look at the ISU-122, which appeared later than the 152-mm SU-152 and ISU-152.
The 122-mm cannon model 1931/37 (A-19) had very good characteristics for its time. The 53-BR-471 armor-piercing projectile with a mass of 25 kg, having accelerated in a barrel length of 5650 mm to 800 m / s, at a distance of 1000 m normally pierced 130 mm armor. At an angle of encounter with the armor of 60 °, at the same range, the armor penetration was 108 mm. The 53-OF-471 high-explosive fragmentation projectile weighing 25 kg, containing 3.6 kg of TNT, also demonstrated good efficiency when firing at armored vehicles. Several times there were cases when, as a result of a 122-mm OFS hitting the frontal part of the Tigers and Panthers, the tanks received heavy damage, and the crew was struck by internal chipping of the armor. Thus, the ISU-122 self-propelled artillery mount was capable of fighting all serial German tanks at real battle distances.
A “self-propelled” modification of the A-19C was developed for installation in the ACS. The differences between this version and the towed one consisted in transferring the aiming organs of the gun to one side, equipping the breech with a receiver tray for ease of loading and the introduction of an electric trigger. In the second half of 1944, the serial production of an improved modification of the gun intended for armament of the self-propelled guns began. The upgraded version received the designation "122 mm self-propelled gun mod. 1931/44 ", and in this version, in addition to the variety of a barrel with a free tube, monoblock barrels were also used. Changes were made to the design of the vertical and horizontal guidance mechanisms aimed at increasing reliability and reducing inertial load. Both guns had a piston bolt. The vertical guidance angles ranged from -3 to + 22 °, horizontally - in the 10 ° sector. The range of a direct shot at a target with a height of 2.5-3 m was 1000-1200 m, the effective firing range at armored vehicles was 2500 m, the maximum was 14300 m. The rate of fire was 1.5-2 rds / min. The ISU-122 ammunition consisted of 30 separate-case loading rounds.
Serial production of the ISU-122 began in April 1944. Self-propelled guns of the first series had one-piece frontal hull armor. ISU-122, produced since the fall of 1944, had frontal hull armor welded from two rolled armor plates. This version of the self-propelled gun was distinguished by an increased thickness of the gun mantlet and more spacious fuel tanks.
Since October 1944, an anti-aircraft gun 12, 7-mm DShK machine gun was mounted in the area of the right hatch. The DShK large-caliber anti-aircraft machine gun turned out to be in great demand during the storming of cities, when it was required to destroy the enemy infantry, hiding among the ruins or on the upper floors and attics of buildings.
The thickness of the frontal and side armor of the hull was 90 mm, the stern of the hull - 60 mm. The gun mask is 100-120 mm. The front of the wheelhouse was covered with 90 mm armor, the side and rear of the wheelhouse were 60 mm. The roof is 30 mm, the bottom is 20 mm.
The mass of the installation in the firing position was 46 tons. Diesel engine with a capacity of 520 hp. could accelerate the car on the highway to 37 km / h. The maximum road speed is 25 km / h. In store down the highway - up to 220 km. Crew - 5 people.
Since May 1944, some heavy self-propelled artillery regiments, previously armed with heavy self-propelled guns SU-152, began to switch to ISU-122. When the regiments were transferred to new states, they were assigned the rank of guards. In total, by the end of the war, 56 such regiments were formed with 21 ISU-152 or ISU-122 self-propelled guns in each (some of the regiments had a mixed composition). In March 1945, the 66th Guards Heavy Self-Propelled Artillery Brigade (65 ISU-122 and 3 SU-76) was formed. Self-propelled guns were actively used at the final stage of the war. According to archival documents, 945 ISU-122 were built in 1944, of which 169 were lost in combat.
Unlike tanks and self-propelled guns produced in the initial period of the war, the ISU-122 self-propelled guns were quite sophisticated and quite reliable. This was largely due to the fact that the main "children's sores" of the engine-transmission group and the chassis were identified and eliminated on the IS-2 tanks and ISU-152 self-propelled guns. The ISU-122 self-propelled gun was quite consistent with its purpose. It could be successfully used to destroy long-term fortifications and destroy heavy enemy tanks. So, during tests at the test site, the frontal armor of the German tank PzKpfw V Panther was pierced by a 122-mm armor-piercing projectile fired from a distance of 2.5 km. At the same time, the A-19C gun had a significant drawback - a low rate of fire, which was limited by a manually opened piston-type bolt. The introduction of a 5th member, a castle member, into the crew, not only did not solve the problem of low rate of fire, but also created additional tightness in the fighting compartment.
Self-propelled artillery installation ISU-122S
In August 1944, the production of the ISU-122S ACS began. This self-propelled gun was armed with a 122 mm D-25S cannon with a semi-automatic wedge gate and a muzzle brake. This gun was created on the basis of the D-25 gun, which was installed in the turret of the IS-2 heavy tank.
The installation of a new weapon led to changes in the design of recoil devices, a cradle and a number of other elements. The D-25S cannon was equipped with a two-chamber muzzle brake, which was absent from the A-19S cannon. A new molded mask with a thickness of 120-150 mm was created. The sights of the gun remained the same: the telescopic TSh-17 and the Hertz panorama. The crew of the self-propelled gun was reduced to 4 people, excluding the castle. The convenient location of the crew in the fighting compartment and the semi-automatic shutter of the gun contributed to an increase in the combat rate of fire up to 3-4 rds / min. There were cases when a well-coordinated crew could make 5 rounds / min. The freed up space was used to accommodate additional ammunition. Although the power of the ISU-122 self-propelled gun did not exceed the IS-2 tank, in practice, the actual combat rate of fire of the self-propelled gun was higher. This is primarily due to the fact that the self-propelled gun had a more spacious fighting compartment and better working conditions for the loader and gunner.
The increase in the rate of fire, which was achieved on the ISU-122S, had a positive effect on the anti-tank capabilities of the self-propelled gun. However, the ISU-122S could not displace the ISU-122 with a 122-mm gun mod. 1931/1944, which was due to the lack of D-25 cannons, which were also used to arm the IS-2 tanks.
Self-propelled guns ISU-122S, actively used at the final stage of the war, were a very powerful anti-tank weapon. But they failed to fully reveal themselves in this capacity. By the time the mass production of the ISU-122S began, German tanks were rarely used for counterattacks and were mainly used in defensive battles as an anti-tank reserve, acting from ambushes.
The use of ISU-122 / ISU-122S in wooded areas and urban battles was difficult due to the long gun. Maneuvering in narrow streets with a long cannon sticking out a few meters in front of an SPG with a front-mounted fighting compartment was not easy. In addition, the driver had to be very careful on descents. Otherwise, there was a high probability of "scooping up" the soil with the tool.
The mobility and maneuverability of the ISU-122 / ISU-122S self-propelled guns was at the level of the IS-2 heavy tank. In muddy conditions, they often did not keep up with the T-34 medium tanks, as well as the SU-85 and SU-100 tank destroyers.
In total, military representatives accepted 1735 ISU-122 (1335 until the end of April 1945) and 675 ISU-122S (425 until the end of April 1945). Serial production of self-propelled guns of this type ended in August 1945. In the post-war period, the ISU-122 / ISU-122S were modernized and operated until the mid-1960s.
