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Soviet Union (1944-1952?)
Heavy self-propelled gun – Estimated 2,410 built
An under-gunned ISU-152
The ISU-122 was a heavy self propelled gun, and de facto tank destroyer. The vehicle came to be because the Soviets were able to produce ISU-152 hulls faster than they could produce their 152 mm (6 in) ML-20S armament. Not wanting to slow down heavy tank production, it was realized that there was a surplus of 122 mm (4.8 in) A-19 guns, and thus the problem was solved – the two were mated. Much like its older brother, the ISU-152, the ISU-122 saw action as a multi-role vehicle, but it was used as a tank destroyer more than the ISU-152 because its 122 mm gun was much more accurate than the 152 mm ML-20S howitzer. However, postwar, the ISU-122 was deemed unsatisfactory, and many were later refitted for other military uses, such as armored recovery vehicle. Many were disarmed, and handed over for civilian purposes, such as working on railways.
The creation of the ISU-122 was a direct result of ISU hulls having production speed stepped up, but their ML-20S armament’s production speed being kept the same. State authorities wanted to speed up tank production, and were not willing to wait for new 152 mm (6 in) guns to be produced. As a result of this lack of armament, the stock of surplus A-19 122mm guns were mounted instead, and, rather handily, the A-19 and ML-20 field guns were both mounted on the same towing carriage (the 52-L-504A), and so the gun mount in the ISU’s hull needed little redesigning to fit the new gun.
The A-19 was modified to fit tanks, and was designated A-19S, but as a result of the manual-piston breech, the rate of fire was reduced from 2.5 to a mere 1.5 rounds per minute. This was hardly an under-armament, because it excelled at providing effective direct fire at enemy heavy tanks – something that the ISU-152 was known for, but did not excel at in reality. Seeing the huge benefit over the ISU-152 for this role, the State Defense Committee accepted the Object 242 (as it was known during tests) as a new design, as opposed to a stopgap improvisation on April 12th, 1944, and the first vehicles left the ChTZ factories in the same month.
When the ISU-122’s production ended seems to be open to debate. According to some sources, production was concluded at the end of 1945, but, according to other sources, most notably, Zaloga’s “IS-2 Heavy Tank, 1944-1973”, production resumed in 1947 until 1952, with 3130 produced, for unstated reasons. It is possible that there were large stocks of A-19 or D-25S guns that needed using up. The total number produced remains unclear, with many sources giving figures not even close to the other. The highest estimate is over 5000, and lowest at roughly 2000.
In the 1950s, many ISU-122s were converted for civilian use (such as on the railways or even reportedly in the arctic as transport vehicles). Many others were converted into ARVs, and some others into heavy rocket launching platforms. However, the few ISU-122s that were not converted were modernized in 1958, similar to the ISU-152 modernization. However, it was not as thorough, and most only received upgraded gun sights and radio sets, with some few getting a new engine. The ISU-122 was totally withdrawn from service by 1960.
Realizing that the A-19S had a slow rate of fire, the famous D-25 gun was later fitted. D-25S production was prioritized to be fitted to IS-2s, but as more became available in late 1944, they were fitted to the ISU hull. This variant passed trials in late 1944 and was referred to as the Object 249 or ISU-122-2. Rate of fire was now 2-3 shots per minute, and even 4 shots per minute with experienced loaders.
The easiest way to spot this variant is by the double baffle muzzle brake or by the ball-shaped gun mantlet. The D-25S’ muzzle brake reduced the recoil force from firing the gun and made working conditions better for the crew, as well as allowing a smaller, lighter gun mantlet being mounted, but with the same effective armor protection due to its round shape. 675 ISU tanks were fitted with the D-25 gun, but because of the huge stocks of the A-19, both the ISU-122 and ISU-122S were produced until the end of 1945.
BTT-1 and ISU-T
These were armored recovery vehicles based on the ISU-122. Because the ISU-122 was effectively redundant after WWII, they were converted for many other uses. The ISU-T was an early version that was made in the early 1950s, by simply removing the gun and placing a metal sheet over the top. However, this was little more than a cheap conversion. In 1959, the BTT-1 was designed as a more serious and better equipped vehicle.
Essentially the same as the ISU-T, they also had any combination of: a basket mounted on the rear deck, a winch, crane, a dozer blade (of various sizes) and other towing equipment. In 1960, modernization of these vehicles took place which saw another generator added to the vehicle to allow welding and field repairs of vehicles. There was also fairly little standardization of the vehicle, with some featuring local modernization with A-frame cranes.
Further details on the vehicle are scarce, but it appears that many different countries used this vehicle, such as Egypt, the USSR, Poland, and Czechoslovakia. Egypt seemed to get their BTT-1s along with a purchase of a regiment of ISU-152s in the early 1960s. At least one was captured by Israel during either the 1967 or 1973 war, and now stands at Yad La-Shiryon Museum.
According to Zaloga, this was a very short-lived project designed with wider tracks and heavier armor. It was designed to be protected against German 88 mm (3.46 in) guns, but it was not accepted into service due to its significantly reduced mobility.
These “BM” or “High Powered” projects were attempts in mid-1944 at Zavod Nr. 100 at making the ISU chassis into a dedicated heavy tank hunter capable of destroying the King Tiger and Jagdtiger. Many designs were made from June 1944 right up to the end of 1945, using various calibers such as 122 mm, 130 mm, and 152 mm. For the 152 mm projects, see the ISU-152 article. None of the “BM” designs were accepted for a variety of reasons, such as poor gun handling, excessively long barrel length (thus making maneuvers in urban areas difficult), the lack of King Tigers (and similarly armored vehicles) expected to be encountered, and the relative sufficiency of ISU-122S and IS-2 tanks at dealing with these heavily armored rarities.
The ISU-130 was built in autumn, 1944 and featured a 130 mm (5.12 in) S-26 gun. This gun is sometimes referred to as a naval gun, but this is not entirely accurate – the S-26 derived from a naval gun, and featured a muzzle brake and horizontal wedges. In October, 1944, the ISU-130 underwent factory trials, and the following month, trials were held at the Polygon. Testing ended in 1945, and the gun was sent to the TaSKB for completion, but the war was over, and the project was disbanded. Its main advantage was that, whilst it provided similar ballistic results to the high powered 152 mm projects, it had smaller shells, which meant the vehicle could carry 25 shells, as opposed to 21. It had a muzzle velocity of 900 m/s, and a range of 500 m, placing it in roughly the middle of all “BM” project guns. It is currently preserved at Kubinka Tank Museum.
The ISU-130 on display at Kubinka.
The Object 243, or ISU-122-1, featured a 122 mm BL-9 gun – one of the infamous BL guns made at OKB-172. It essentially looked like a longer version of the A-19S, although the gun mantlet had some tweaking to fit the longer and heavier gun. It could carry 21 AP rounds. Its muzzle velocity was 1007 m/s, which was the highest of all “BM” guns.
The ISU-122-3 (-2 was the ISU-122S with the D-25S) was derived from the ISU-130. It featured essentially a 122 mm version of the 130 mm S-26, which was designated the S-26-1. It had practically the same ballistics as the BL-9, but it had a muzzle brake, different components, and the chassis used a different mantlet. It could fire 1.5-1.8 rounds per minute, and had a muzzle velocity of 1000 m/s. It underwent field tests in November, 1944, but according to sources, something (probably the mantlet or gun mechanism) was simply not strong enough to withstand firing the gun. The gun project was totally completed in June, 1945, but was abandoned due to the war’s end.
Photograph of an ISU-122-3. Its muzzle brake is very distinguishable, compared to the ISU-122-1, which featured a similar length gun, but no muzzle brake.
Another supposed ISU-130 name is scarcely referred to in Zaloga’s “Soviet Tanks and Combat Vehicles of World War Two“. According to the book, it was a design that came about towards to the end of the war by Dukhov’s team. It was either an ISU-122 or IS-3 chassis (he later contradicts himself, but the drawing certainly appears to show an IS-2/ISU-122 chassis) with a 130 mm naval gun. It was not produced until after the war, and strongly resembled the Object 704. It is more than likely that this was a version of the above, and due to the lack of access to Kremlin archives at the book’s publication date, it is probably an inaccurate story and depiction.
Drawing of an “ISU-130” as taken from Zaloga’s “Soviet Tanks and Combat Vehicles of World War Two”. It closely resembles the Object 704, and appears to be based on an IS-2/ISU-122. Due to the lack of access to Kremlin archives at the book’s publication date, it is probably an inaccurate depiction.
The ISU-122 in action
The ISU-122 was a multi-role tank, much like the ISU-152. However, it had the advantage of a fairly accurate gun, with excellent AT capabilities. At a range of 1000 m, the ISU-152 could penetrate 120 mm (4.72 in) of armor (which was the Tiger’s maximum armor thickness), but the ISU-122 could penetrate 160 mm (6.3 in) (which is much closer to the King Tiger’s 185 mm/7.28 in maximum armor thickness), and was more accurate.
Whilst the ISU-122 tended to use armor piercing rounds, due to supply issues, they often found themselves firing high-explosive shells designated OF-471. These shells weighed 25 kilograms, had a muzzle velocity of 800 m/s, and had a 3 kilogram TNT charge. This proved absolutely excellent for AT duties as the explosion and shock-wave sent across the mechanisms on the targeted tank were sometimes enough to knock it out even without penetrating!
However, its AT capabilities were rarely taken advantage of due to the tactics used by heavy SPG regiments. It was used, like the ISU-152, for direct fire, and there was no practical distinction between the ISU-152 and ISU-122 at the time.
Many ISU-122s were often fielded in mixed units with the ISU-152, despite attempts by Red Army Commanders to avoid this within one tank regiment or at least a tank brigade. There were two main reasons for this – the first being that two sets of calculations would be needed for indirect fire orders, and the second being that the tanks took different ammunition types, which would cause supply problems as two different shell types would need transporting.
Aside from that minor problem, the ISU-122 fared very well in combat. Being based on the IS-2 hull, it had excellent armor performance, which was previously a problem for many Soviet SPGs, such as the SU-76 and SU-85, which would not be able to handle much attention from enemy armor or AT guns.
Duties as a self-propelled howitzer with indirect fire were rare, but not unheard of. This was usually done during quick advances, when support from field artillery was not available. The gun had a maximum range of 14 km, which made it a viable role to take on, but it was simply not a common tactic.
In urban combat, the ISU-122 fared marginally less well than the ISU-152 for two reasons – first, the longer gun barrel made traversing difficult in small, rubble filled streets, whereas the ISU-152, with its smaller gun, did not have this problem. Secondly, the smaller, 25 kg HE shell, was not as destructive as the shells fired from the ISU-152. The ISU-152 was given a 43.56 kg HE shell, a 48.78 kg AP shell, and even a 56 kg long range, concrete-piercing shell which could obliterate enemy positions.
As mentioned earlier, the ISU-122 only had AP and HE shells, which were less destructive and therefore not as effective as the ISU-152. Despite this, it was viewed as a good urban assault gun (again, there was practically no distinction between the ISU-122 and ISU-152 by Red Army Command), and HE shells were usually sufficient at taking out enemy pillboxes, fortified buildings, and trenches. Even considering that the ISU-122’s shells were not as destructive, it must be remembered that the ISU-122 had just over twice the rate of fire than the ISU-152, even without experienced loaders.
After the war, most ISU-122s survived, although many were, as mentioned, scrapped, or converted in the 1950s and 1960s. Despite those programs, some are still preserved today and at least five stand in museums across Eastern Europe. Many others are preserved as memorials.
ISU-122 in Chinese service
Once the Red Army left Dailan, Liaoning Province, in former Manchuria, all weapons from that area were sold to the People’s Liberation Army. An unknown number of ISU-122 tanks (according to an available photo of a parade, at very least, six) were sold to the People’s Republic of China, along with SU-76s, ISU-152s, T-34/85s, T-34/76s, SU-100s, and SU-76s. It is unknown if any ISU-122S tanks were sold along with these.
ISU-122 of the 59th Independent Breakthrough Tank Regiment, 9th Mechanized Corps, 3rd Guards Tank Army, in a strange winter livery, Ukrainian SSR, 1944.
|Dimensions (L-w-h)||9.85 x 3.07 x 2.48 m (32.3 x 10 x 8.1 ft)|
|Total weight, battle ready||45.5 tonnes|
|Crew||4 or 5 Commander, Gunner, Driver, Loader and an optional second loader)|
|Propulsion||12 cyl. 4 stroke diesel, V-2IS 520 hp|
|Speed (road)||37 km/h (23 mph)|
|Range||220km (137 miles)|
|Armament||122 mm (4.8 in) A-19S tank gun (ISU-122) or 122 mm (4.8 in) D-25S (ISU-122S)
DShK 12.7 mm (0.3 in) AA machine-gun (250 rounds)
|Armor||30-90 mm, plus 120 mm mantlet (1.18-3.54 +4.72 in)|
|Total production||2410 (1735 ISU-122, 675 ISU-122S), 1944-1945. Possibly at least 1000 more 1947-1952, although sources give wildly varying different figures.|
An article by Will Kerrs
“Russian Tanks of World War II, Stalin’s Armoured Might“, by Tim Bean and Will Fowler.
“Soviet Tanks and Combat Vehicles of World War Two” by Steven J. Zaloga and James Grandsen.
“IS-2 Heavy Tank 1944-1973” by Steven J. Zaloga
ISU-122, summer, 1944
ISU-122, unknown unit, east Prussia, 1944
ISU-122, unknown unit, Germany, 1945
ISU-122, winter camouflage, Germany, 1944-45
ISU-122 camouflaged, unknown unit, 1944
ISU-122, 338th Guards Kirovgradarsky heavy self propelled regiment, 1945
ISU-122S, unknown unit, Poland, summer, 1944
ISU-122S, Berlin, April, 1945
ISU-122S, Hungary, March, 1945
ISU-122 of the People’s Liberation Army, on parade in Beijing, 1954.
BTT-1 heavy duty armoured recovery vehicle after the war. Many were resold to the Egyptian Army, well into service in the 1980s.