ISU-152

ISU-152BM (ИСУ-152БМ), sometimes referred to as ISU-152BM-1 or ISU-152-1, with the factory designation Object 246 (Объект 246), was a single prototype developed in April 1944 in Factory No. 100 in attempt to increase the firepower of the ISU-152. The "BM" ("БМ") in the designation stands for "High-Powered" ("Большой Мощности"). The main purpose of the ISU-152BM was to fight against heavily armored tank destroyers such as the Elefant and the Jagdtiger. It was armed with the 152.4 mm BL-8 (БЛ-8) long-barreled gun, which unlike the ISU-152's gun was not a gun-howitzer. The gun had a maximum range of 18,500 metres (20,232 yd), with the 43.56-kilogram (96.0 lb) high-explosive shell which had a muzzle velocity of 880 metres per second (2,887 ft/s). The overall length of the gun was over 8 metres (26 ft), with a barrel length of 7,620 millimetres (300 in) (50 calibers). The armor-piercing round, weighing 48.78 kilograms (107.5 lb), had a muzzle velocity of 850 metres per second (2,800 ft/s). During test firing at armour plates with different thicknesses, the ISU-152BM successfully penetrated a maximum of 203 millimetres (8.0 in) of RHA at 90° at ranges of up to 2,000 metres (2,187 yd). However, during trials in July 1944, the gun showed some deficiencies, such as being difficult for the crew to operate, unreliability of the muzzle brake and the breech block, and unsatisfactory performance of the shells. In addition, the gun, protruding far forward of the hull front, limited the maneuverability of the vehicle. The self-propelled gun carried 21 rounds of two-piece (shell and charge) ammunition, and had a rate of fire of 2 rounds per minute. It used the engine, transmission, running gear, and electric equipment of the ISU-122. In August 1944 the BL-8 gun was replaced with the improved 152.4 mm BL-10 (БЛ-10) long-barreled gun, with a slightly shorter barrel of 7.392 metres (24.25 ft) (48.5 calibers). This vehicle gun was designated ISU-152-2 (ИСУ-152-2). The factory designation was Object 247 (Объект 247). It was also equipped with external fuel tanks. The gun had a modified muzzle brake and a semi-automatic breech block. It had a rate of fire of 3 rounds/min. The BL-10 had a maximum range of 18,000 metres (19,685 yd), with the 43.56-kilogram (96.0 lb) high-explosive shell. In December 1944 the ISU-152-2 underwent trials, revealing the barrel strength and the angle of horizontal guidance were unsatisfactory. The gun was sent for further improvement, but it was not completed before the war ended. The vehicle was never adopted. After the war, the final and most improved, third modification of ISU-152-2 was completed. The gun had a maximum range of 19,500 metres (21,325 yd), using a 48.5-kilogram (107 lb) high-explosive shell with a muzzle velocity of 880 metres per second (2,887 ft/s).

Object 704.

Object 704 (Объект 704) was the factory designation for a prototype self propelled gun developed in 1945. Also known as the Kirovets-2, it was developed on the chassis of the Kirovets-1, the initial prototype of the project that became the IS-3. The overall height of the vehicle was reduced to 2,240 millimetres (7.35 ft), which was compensated with an increased width of the superstructure. It was armed with the 152.4 mm ML-20SM model 1944 (МЛ-20СМ обр. 1944 г.) gun-howitzer, with a barrel length of over 4.5 metres (15 ft) (29.6 calibers) and no muzzle brake. It had a maximum range of 13,000 metres (42,651 ft). The self-propelled gun carried 20 rounds of two-piece (shell and charge) armour-piercing and high-explosive ammunition. The armour-piercing round, weighing 48.78 kilograms (107.5 lb), had a muzzle velocity of 655 metres per second (2,149 ft/s). The rate of fire was 1-2 round/min. Object 704 had four hatches at the superstructure roof and one emergency hatch at the bottom of the hull behind the driver's seat, which had an armoured cover. The self-propelled gun carried two external 90-litre (19.8 imp gal; 23.8 US gal) fuel tanks, not connected to the supply system. The secondary armament of the fighting vehicle consisted of two 12.7×108 mm DShK machine guns, one anti-aircraft and one co-axial. The protection was increased by placing thicker armour at more radical angles. In the area of the gun, where the mantlet combined with the hull front behind it and the housing of the recoil mechanism, the armour thickness was 320 millimetres (13 in). Object 704 was the best protected of all experimental or production Soviet self-propelled guns of the Second World War. However, the radical incline of the superstructure walls combined with the increased recoil of the gun, due to the lack of a muzzle brake, significantly complicated the work of the crew, and for this reason it was not adopted.[6][7]

ISU-152K, Victory Park, Moscow, Russia.

Object 241K (Объект 241К) was the factory designation for a modernised variant of the wartime ISU-152, developed in 1956. It used a new engine, that of the T-54, with a cooling system and a heater. The capacity of the main internal fuel tank was increased to 920 litres (202 imp gal; 243 US gal), which added 500 kilometres (311 mi) more to the vehicle′s range on a road. The ammunition capacity was increased to 30 rounds after the removal of an additional internal fuel tank placed in the crew compartment. The gun had a maximum range of 13,000 metres (14,217 yd). It received a new commander's cupola, and also new sights. The running gear used many elements of the T-10. The mantlet had additional armor ring protecting the sight. Some of the ISU-152Ks received an additional 15 mm armour plate welded on top of the 60 mm armour plate covering the mantlet above. Also, some of them received an additional armour plate welded on the upper mantlet front. The modernisation was carried out in the Leningrad Kirov Plant.[3]

ISU-152M was the final variant of ISU-152, developed in 1959. The work was now transferred to the Chelyabinsk Kirovsk Plant. This modernisation was parallel to the IS-2M program and the ISU-152M used many elements of the tank. The factory designation was Object 241M (Объект 241М). The innovations included night vision sights, increased ammunition stowage for the 12.7 mm machine gun, which was replaced by the improved DShKM, and internal automotive improvements. It had the same new commander's cupola and sights as the ISU-152K. It also had the same main internal fuel tank capacity, 920 litres (202 imp gal; 243 US gal), adding 500 kilometres (311 mi) more to the vehicle′s range on a road compared to the ISU-152, and an increased ammunition capacity to 30 rounds due to the removal of an internal fuel tank. The gun had a maximum range of 13,000 metres (14,217 yd). The ring protecting the sight was present, and the armour of the upper mantlet front was further increased with a thicker additional armour plate. The ISU-152M had the same V-54K engine with a heater, but lacked the cooling system.[8]

As a heavy assault gun, the ISU-152 was an extremely valuable weapon in urban combat operations such as the Battle of Berlin, Budapest and Königsberg. The vehicle's excellent armour protection finally provided the 152.4 mm gun with good protection from most German anti-tank guns, allowing it to advance into the face of direct anti-tank fire, while the huge, low velocity, high-explosive rounds were excellent at blasting open even the most heavily fortified and reinforced enemy strongpoints. Such actions would be much more dangerous and much less effective for a conventional towed artillery piece, with their high crew exposure and low mobility, or even a tank, with their smaller main guns. When supporting tanks, the usual tactics of the ISU-152 were to be used in the second line of the attack order, 100 to 200 metres (110 to 220 yd) behind the attacking tanks, which were usually IS tanks with equal mobility.

The ISU-152, like the earlier SU-152 and contemporary ISU-122, was employed by Independent Heavy Self-propelled Artillery Regiments. Between May 1943 and 1945, 53 of these regiments were formed. Many of them were re-formed tank regiments, and employed similar direct fire tactics as used by tanks when supporting infantry. Each of the heavy regiment had 21 guns, divided into four artillery batteries of five vehicles and the commander's vehicle. For support, these heavy regiments had some supplementary unarmoured vehicles such as trucks, jeeps, or motorcycles. In December 1944, Guards Heavy Self-propelled Artillery Brigades were formed, to provide heavy fire support to the tank armies. They were organized along the model of tank brigades, each with 65 ISU-152 or ISU-122 self-propelled guns.

To minimize the risks of being knocked out by Panzerfaust-equipped units during urban operations, the ISU-152 usually acted in one- or two-vehicle detachments alongside infantry squads for protection. The infantry squad would include a specialist sniper (or at least a sharpshooter), some submachine gunners and sometimes a flamethrower. The ISU-152's heavy-calibre DShK machine gun was also useful for targeting Panzerfaust gunners hiding on upper floors of city buildings or behind protective cover and defensive barricades. Effective teamwork between the ISU-152 crew and supporting infantry allowed them to achieve their goals with minimal losses, but if such tactics were not adhered to, the attacking vehicles were easily attacked and destroyed, usually through the weaker armor on the roof or rear compartment.

Front view of ISU-152

The ISU-152 could also operate as an effective heavy tank destroyer. Though it was not designed for the role, the vehicle inherited the nickname Zveroboy ("beast killer") from its predecessor, the SU-152, for its ability to reliably kill the best protected German fighting vehicles; the Panther tank, the Tiger I and Tiger II tanks, and even the rare Elefant and Jagdtiger tank destroyers. The sheer weight of the 152.4 mm shells resulted in an extremely low rate of fire, only one to three rounds per minute, and were not as accurate at long range as high-velocity tank and anti-tank guns. However, the massive blast effect from the heavy high-explosive warhead was capable of blowing the turret completely off a Tiger tank. A direct hit usually destroyed or damaged the target's tracks and suspension, immobilizing it. While the low-velocity 152mm shell did not generally penetrate heavy armor, it frequently killed or severely wounded the crew through spalling (splintering) inside the hull as well as injuries caused by blast concussion. Due to the brittle nature of German tank steel during the latter stages of the war, it was common for impacted armor plates to shatter from the concussive blast, or for weld lines to break, allowing the entire armor piece to fall away. Surviving crew were often left with an immobilized vehicle which had to be hurriedly abandoned before being destroyed.

For anti-tank operations following the July 1943 Battle of Kursk, armour-piercing ammunition was developed, with an eye towards giving the howitzer a more traditional anti-tank capability. However, these rounds were expensive, in short supply, and only moderately more effective than the standard non-penetrating high-explosive round. As a howitzer the ML-20S exchanged velocity and accuracy for throw weight and distance, and was not intended to compete with true anti-tank guns. Sometimes the concrete-piercing ammunition was used for the anti-tank role. A primitive shaped charge ammunition, with a 27.44-kilogram (60.49 lb) shell, was also developed. It had a maximum penetration of 250 mm of RHA at 90°, but it was not used during the war.

The ISU-152's 90 mm of sloped frontal armor, in contrast to the SU-152's 65 mm, provided excellent frontal protection from the 75mm KwK 40 gun of the ubiquitous Panzer IV and StuG family at all but the closest ranges, while also forcing the original Tiger I, with its vaunted 88 mm KwK 36 gun, to close to medium ranges in order to successfully penetrate the vehicle, negating its traditional long-range superiority and putting it within effective range of the Soviet T-34-85 medium tanks.

The ISU-152 was not a true purpose-built tank destroyer. It had a very low rate of fire compared with specialised tank destroyers such as the German Jagdpanther or the Soviet SU-100, which could manage a brief burst of five to eight rounds per minute. However, prior to the introduction of the SU-100 it was the only Soviet armored vehicle capable of tackling the German heavy tanks with any kind of reliability, and its ability to satisfy multiple roles meant it was produced in far greater numbers than the SU-100. Attention to camouflage, quick relocation between firing positions, and massed ambushes of four or five vehicles firing in salvo at a single target's flanks reduced the disadvantage of the low rate of fire.

The ISU-152 was also sometimes used as self-propelled artillery for support on the battlefield and preparatory bombardments, though it had a medium range of fire and a slow speed of reloading. The Soviet army had not developed specialized vehicles for this purpose. Their tank and mechanized units were well equipped with towed artillery, but the towed guns were very vulnerable while moving and they could not support tanks and motorized infantry during rapid advances into enemy positions, especially when they lacked the armored fully enclosed design of vehicles like ISU-152.

The internal stowage was limited to only 20 or 21 rounds of ammunition, with extra rounds often stowed on the rear deck. Replenishing the vehicle's ammunition supply took over 40 minutes and required a very strong loader, due to the large size and weight of the shells - over 40 kg (88 lb). The ST-10 telescopic sight used for direct fire was graduated up to 900 m (3,000 ft). A second, panoramic, sight was used for direct fire up to 3,500 m (3,800 yd) range[9] no direct fire. However, it was problematic for the gunner to switch between the two. To compensate it was simpler to concentrate the fire of several vehicles onto the target, sacrificing accuracy for volume of firepower. The high-explosive shells were large enough to take out even a heavily armoured vehicle, or a fortification with the even heavier long-range concrete-piercing shells. The usual complement of ammunition was 13 high-explosive and 7 armour-piercing or concrete-piercing.

The armor penetration can vary between ammunition batches and different rolled homogeneous armour.

In June 1944, during the Continuation War, a captured ISU-152 was used by the Finnish military. It was abandoned during the counter-attack at Kärstilänjärvi after receiving numerous shots from Soviet T-34-85 medium tanks. This was a direct result of the Finnish crew's lack of experience and training with the ISU-152. Another captured one was repaired in Varkaus, Finland, but never saw combat.

Polish ISU-152 displayed at the Muzeum Polskiej Techniki Wojskowej in Warsaw.

In 1944, more than 30 ISU-152s were delivered to the People's Army of Poland. Shortly afterwards, the Polish military created the 25th Polish Self-Propelled Artillery Regiment, which consisted of 10 ISU-152s and 22 ISU-122s. As part of the 1st Polish Tank Corps (which operated both T-34-76 and T-34-85 tanks), the regiment took part in combat action along the River Nysa, located in southwestern Poland in March 1945. In the early months of 1945, the Polish command began to form another ISU-152 regiment, but with too few vehicles, the newly-formed 13th Polish self-propelled artillery regiment received two ISU-152s and two batteries comprising SU-85s. This regiment took part in the Battle of Berlin between April and May of 1945.

Post-WWII, ISU-152s remained in service with the Polish military until the early 1960s.

As part of the Soviet Union's military assistance to friendly or pro-Soviet countries around the world, a few ISU-152s were transferred to the Czechoslovakian military after World War II, which operated them until the end of 1950s. For several decades it was the heaviest armored vehicle in the Czechoslovak People's Army, which used these to test newly-developed anti-tank obstacles.

One captured during World War II.[10] The Romanian Army had received 20 ISU-152s during the 1950s; these were assigned to the artillery units of the 6th, 7th and 57th tank divisions of the Romanian Army. They were known as T-152 in Romanian service.[11][12]

The Yugoslav Army had only one ISU-152 in its inventory. This sole vehicle was abandoned by units of the Soviet Red Army's 2nd Ukrainian Front in 1944. In 1946, members of the Yugoslav 2nd Tank Brigade's first battalion, led by technical officer Stojimir Ilijevic – Guerrilla, recovered the self-propelled gun after five days of work. As a unique vehicle it was used by the Army's Tank School at Bela Crkva. After it was withdrawn from service, this single Yugoslav ISU-152 ended up as a practice target at the Manjača firing range.[13]

In 1955, the Soviet Army moved out from Dalian in northeastern China, officially ending 10 years of military occupation. All weapons and armaments left behind by the Soviet Union were sold to the Chinese People's Liberation Army, including 67 ISU-152s; 45 were given to the newly-created 1st Mechanized Division of the PLA.

During and after the Korean War, ISU-152s were operated by the Korean People's Army of the DPRK. North Korea reportedly still uses ISU-152s in both active and reserve units, however, the actual number is unknown.

Captured Egyptian ISU-152 in the Yad la-Shiryon Museum, Israel.

In the early 1960s the Egyptian military received at least one regiment of ISU-152s. They were used during the Arab-Israeli conflicts between 1967 and 1973. They proved mostly ineffective and several were captured by the Israeli Defence Forces; one is now on display in Yad la-Shiryon.[3]

A wrecked ISU-152 at Camp Fallujah, Iraq.

A few surviving examples were operational during the Iran–Iraq War and First Gulf War.