The ISU-152
self-propelled gun combined three battle roles: heavy
assault gun, heavy
tank destroyer and heavy
self-propelled artillery. The 152.4 mm gun used a number of powerful (shell and charge) ammunition. Some of these ammunition had a 43.56 kg high-explosive shell, or a 48.78 kg armour-piercing shell, or the heaviest of all, the 53-G-545 (53-Г-545) long-range concrete-piercing ammunition with a 56 kg shell. The ISU-152 was used for infantry and tank support in attacking fortified enemy positions in a direct-fire role, for artillery support on the battlefield in an indirect-fire role and for engagement against armored vehicles in a direct-fire role. The ISU-152 was also used by
Liquidators during cleanup after the
Chernobyl Disaster for demolition.
Heavy assault gun 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, 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.
Heavy tank destroyer 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 two to three rounds per minute, and less accuracy at long range than 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 high-explosive 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 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.
Self-propelled artillery 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 . The ST-10 telescopic sight used for direct fire was graduated up to . A second, panoramic, sight was used for direct fire up to range 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. ==Soviet military service==