The ISU-122 was a Soviet assault gun used during World War II, primarily in an anti-tank role.The ISU-122 was used as a powerful assault gun, self-propelled howitzer, and long-range tank destroyer, in the same way as the typical SU-152 and ISU-152 heavy self-propelled guns. However, these vehicles differ in their combat use.The ISU-122's primary application is as a tank destroyer, while the SU / ISU-152 is more oriented to the assault gun role.The ISU-122 has the same hull as the IS-2, with good armour performance, but performs very well with high explosive rounds.The 122mm gun has great potential, although it can be used in a variety of roles due to the available projectiles and lack of accuracy, the gun's capability was reduced.In 1944, the BR-471 was the only available armour-piercing round. An improved version, the BR-471B (??-471?), was developed in early 1945, but was not available in quantity until after the end of World War II. In extreme cases, the ISU-122 used OF-471 (??-471) high-explosive shells to engage heavy enemy armour. These shells had a mass of 25 kg, a muzzle velocity of 800 m/s, and a 3 kg TNT charge. The mechanical impact and explosion are usually sufficient to knock out enemy armoured fighting vehicles without any armour penetration.

In urban combat, the ISU-122 was used as an assault gun, but was less efficient than the SU/ISU-152. Overall, Red Army commanders considered the ISU-122 to be a good assault gun.The OF-471 projectile was powerful enough against unprotected and entrenched infantry, bunkers and fortifications. In urban combat, the long barrel of the 122mm cannon sometimes makes manoeuvring difficult.

The use of the ISU-122 as a self-propelled howitzer is rare, although its maximum range exceeds 14 km. Typically, the ISU-122 provides indirect fire to the enemy during rapid advances without towed gun support.