ISU-122
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The ISU-122 (acronym of'' Istrebitelnaja - or Iosif Stalin-based - Samokhodnaya Ustanovka 122'') was a
Soviet The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...
assault gun An assault gun (from , , meaning "assault gun") is a type of armored infantry support vehicle and self-propelled artillery, mounting an infantry support gun on a protected self-propelled chassis, intended for providing infantry with heavy di ...
used during
World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
, mostly in the anti-tank role.


History and purpose

A prototype of the ISU-122 (in Russian ИСУ-122) heavy self-propelled gun was built at the Chelyabinsk Kirov Plant (''Chelyabinskiy Kirovskiy Zavod (ChKZ)'',
Chelyabinsk Chelyabinsk; , is the administrative center and largest types of inhabited localities in Russia, city of Chelyabinsk Oblast, Russia. It is the List of cities and towns in Russia by population, seventh-largest city in Russia, with a population ...
, Russia), in December 1943. The design shared the chassis of the ISU-152 self-propelled gun and differed only in armament, having an A-19S 122-mm gun as its main weapon instead of the ISU-152's ML-20S gun-howitzer. Towed versions of these guns used the same carriage: 52-L-504A (Russian designation 52-Л-504А), so installation of an A-19 instead of an ML-20 gun was not a difficult task. After completing development of the ISU-152, ChKZ engineers mounted the A-19 gun on the ISU-152 chassis to create ''"Object 242"'' — the first ISU-122 prototype. It was successfully tested, but not immediately launched into mass production. At that time, all ISU hulls were being equipped with the ML-20S gun-howitzer, but the production of hulls increased quickly and there was a lack of ML-20S tubes in the beginning of 1944. State authorities ordered these uncompleted hulls armed with an A-19 gun (specifically with the A-19S variant, slightly modified for the self-propelled gun mount). A further advantage of rearming the ISU was increased direct fire range against heavy German tanks. For these reasons, the State Defense Committee adopted ''Object 242'' for
Red Army The Workers' and Peasants' Red Army, often shortened to the Red Army, was the army and air force of the Russian Soviet Republic and, from 1922, the Soviet Union. The army was established in January 1918 by a decree of the Council of People ...
service as the ISU-122 on 12 March 1944. In April 1944, the first series ISU-122 left the ChKZ production lines. The A-19S gun had a manual-piston breech, which reduced the rate of fire from 2.5 to 1.5 shots per minute. Soviet designers developed the D-25 by modernizing the A-19S's breech, creating a semi-automatic variant of the 122-mm gun. The D-25 gun was installed in IS-2 tanks as a priority, but in September 1944 became available for self-propelled guns. The prototype ISU vehicle, armed with a D-25S was designated ''"Object 249"'' and successfully passed plant and state testing. The fire rate was improved to 2 to 3 shots per minute and with two strong experienced loaders the rate of fire reached 4 shots per minute. Due to the muzzle brake reducing recoil forces, the D-25 had a smaller recoil buffer than the A-19. This improved the crew's work conditions and allowed for a smaller, lighter gun shield with the same armour thickness. After testing, ''Object 249'' was immediately launched in mass production as the ISU-122S (ИСУ-122С) self-propelled gun. However, the original ISU-122 remained in production (along with the ISU-152) due to a large stock of A-19 guns (the ML-20 and D-25 came directly from artillery factories). Mass production of the ISU-122 and ISU-122S ceased at the end of 1945. ChKZ produced 1,735 ISU-122 and 675 ISU-122S variants in total.Solyankin et al. ''Soviet heavy self propelled guns 1941—1945'', pp. 19, 24 After World War II, many surviving ISU-122s were rebuilt as very large calibre gun chassis or supply vehicles. The small number of ISU-122s that kept their original armament were modernized in 1958. This modernization was not as complete as that of the ISU-152. Most ISU-122s did not receive a new engine, only upgraded gun sights and radio sets. In the beginning of 1960, the ISU-122 was withdrawn from Soviet Army service (the ISU-152 served much longer). Some disarmed ISU-122s were transferred to civil organizations, to be used as emergency vehicles on Soviet railways or as tracked transport in Arctic areas of the Soviet Union. However, most ISU-122s (both variants) remained in service longer in Warsaw Pact states and, with unconfirmed reports, in service in North Korea and China, having both variants.


Variants

Some vehicles were fitted with a 12.7 mm
DShK The DShK M1938 (Cyrillic: ДШК, for ) is a Soviet heavy machine gun. The weapon may be vehicle mounted or used on a tripod or wheeled carriage as a heavy infantry machine gun. The DShK's name is derived from its original designer, Vasily Degtya ...
anti-aircraft machine gun. *ISU-122S - In later models, 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. The ISU-122S model was coded 'type 249' by the German's in their reporting.


Construction and design

Construction of the ISU-122 and ISU-152 is the same except for the gun mounting, sights and ammunition stowage. The A-19S or D-25S cannons of the ISU-122 had 18 degrees elevation angle and 30 rounds of ammunition (the ISU-152 had 20 degrees and 20 rounds respectively). The A-19S cannon was equipped with an ST-18 (СТ-18) telescopic sight and the D-25S cannon was equipped with a TSh-17 (ТШ-17) sight. Both types of sights had maximal exact targeting distance of 1.5 km (the ISU-152 could manage only 900 m). Maximum direct fire range of the A-19S or D-25S cannons was 5 km, much further than these sights' targeting abilities. For direct or indirect firing on distances over 1.5 km the gunner used the second, panoramic sight. The ISU-122 had a five-man crew; their location and roles were identical to those of ISU-152 crewmen. The ISU-122S was used with either four- or five-man crews since the semi-automatic breech allowed for a reasonable fire rate with a crew of four; the place of the absent loader was often taken up with additional ammunition. With a five-man crew (two loaders), the ISU-122S demonstrated a better fire rate than with four men.


Organization

The organization of military units utilizing the ISU-122 was the same as with the ISU-152. Soviet Army commanders tried not to mix the ISU-122 and the ISU-152 in one regiment or brigade, although there were some units equipped with both types. The different armament of the ISU-122 and the ISU-152 caused problems with ammunition supplies and logistics. Another disadvantage of mixed-type units was a doubling of the calculations required for massed indirect fire.


Combat history

The ISU-122 was used as a powerful assault gun, a self-propelled howitzer, and a long-range
tank destroyer A tank destroyer, tank hunter or tank killer is a type of armoured fighting vehicle, predominantly intended for anti-tank duties. They are typically armed with a direct fire anti-tank gun, artillery gun, also known as a self-propelled anti-ta ...
, the same as with the SU-152 and ISU-152 heavy self-propelled guns in general. However, these vehicles differed in their combat use. The primary application of the ISU-122 was as a tank destroyer, while the SU/ISU-152 tended more towards the assault gun role. With the same hull as the IS-2, the ISU-122 had good armour performance but very good performance with high-explosive rounds. The 122-mm gun had great potential, although the gun's abilities were somewhat reduced by the available projectiles and its lack of accuracy. In 1944, the BR-471 was the sole armour-piercing round available. An improved version, the BR-471B (БР-471Б), was developed in early 1945, but was available in quantity only after World War II ended. In extremis, the ISU-122 engaged enemy heavy armour with OF-471 (ОФ-471) high explosive projectiles. These shells had a mass of 25 kg, a muzzle velocity of 800 m/s, and were equipped with a 3 kg TNT charge. Mechanical shock and explosion was often enough to knock out enemy AFVs without any armour penetration. For urban combat, ISU-122s were utilized as assault guns, but with a lower efficiency in comparison to the SU/ISU-152. In general, Red Army commanders viewed the ISU-122 as a good assault gun. The OF-471 projectile was powerful enough against unprotected and entrenched infantry, pillboxes, and fortified buildings. In urban combat, the long barrel of the 122 mm cannon sometimes made maneuvering difficult. Use of the ISU-122 as a self-propelled howitzer was rare, although its maximum range of fire exceeded 14 km. Usually, the ISU-122 delivered indirect fire to the enemy during rapid advances when support from towed artillery was not available.


Surviving examples

Most of the ISU-122s produced survived the Second World War and examples remain, but only a few of the surviving ISU-122s kept their initial appearance. Many were rebuilt or scrapped in the mid 1960s. The number of ISU-122s preserved in museums and memorials is substantially lower than surviving ISU-152s. ISU 122s can be seen in the Military Historical Museum of Artillery, Engineers and Signal Corps in
St Petersburg Saint Petersburg, formerly known as Petrograd and later Leningrad, is the List of cities and towns in Russia by population, second-largest city in Russia after Moscow. It is situated on the Neva, River Neva, at the head of the Gulf of Finland ...
, the
Kubinka Tank Museum The Kubinka Tank Museum (Центральный музей бронетанкового вооружения и техники - Tsentral'nyy Muzey Bronetankovogo Vooruzheniya I Tekhniki -Central Museum of Armored Arms and Technology) is a larg ...
, the Central Museum of the Russian Army, the National Museum of the History of Ukraine in the Second World War in
Kyiv Kyiv, also Kiev, is the capital and most populous List of cities in Ukraine, city of Ukraine. Located in the north-central part of the country, it straddles both sides of the Dnieper, Dnieper River. As of 1 January 2022, its population was 2, ...
(where it is an ISU-152 crudely modified with spare D-25T gun, labeled as ISU-122) and other tank museums and World War II memorials in Poland and
Belarus Belarus, officially the Republic of Belarus, is a landlocked country in Eastern Europe. It is bordered by Russia to the east and northeast, Ukraine to the south, Poland to the west, and Lithuania and Latvia to the northwest. Belarus spans an a ...
.


Operators

* * * *


See also

*
List of Soviet tanks Below is a list of tanks and other armoured fighting vehicles of the Russian empire, Soviet Union, the Russian Federation, and Ukraine. Imperial Russia, World War I Armored tractors *Gulkevich's armored tractor *F. Blinov armored tractor *Wa ...
- covers all periods


Tanks of comparable role, performance and era

* Ho-Ri Japanese proposed tank destroyer, only mock-up scale model were built *
Elefant Elefant ( German for "elephant") was a heavy tank destroyer (self propelled anti-tank gun) used by German ''Panzerjäger'' (anti-tank units) during World War II. Ninety-one units were built in 1943 under the name Ferdinand (after its designer F ...
German tank destroyer, entered service in 1943 *
Sturer Emil The 12.8 cm ''Selbstfahrlafette auf'' VK 30.01(H) ''"Sturer Emil"'' (German for "Stubborn Emil"), also called ''Panzer Selbstfahrlafette'' V (Pz.Sfl. V), was an experimental World War II World War II or the Second World War ...
German tank destroyer, entered service in 1942


Notes


Sources

* Solyankin A. G., Pavlov M. V., Pavlov I. V., Zheltov I. G. — ''Soviet heavy self-propelled guns 1941—1945'', Moscow, Printing centre «Exprint», 2005, 48 pp.  (Солянкин А. Г., Павлов М. В., Павлов И. В., Желтов И. Г. ''Советские тяжёлые самоходные артиллерийские установки 1941-1945 гг.'', М. ООО Издательский центр «Экспринт», 2005, 48 с. ) *


External links


ISU-122 on BattleField.Ru

ISU-122 on Vasiliy Chobitok's ArmorSite
(articles by A. Meretzkov and A. Sorokin) {{DEFAULTSORT:Isu-122 World War II tank destroyers World War II assault guns Assault guns of the Soviet Union 122 mm artillery Military vehicles introduced from 1940 to 1944 World War II armoured fighting vehicles of the Soviet Union Tracked self-propelled artillery