The ISU-152 is a heavy assault gun, fielded by the Soviets.
The Soviet Army first developed a mobile version of their 152mm ML-20 gun-howitzer as a heavy assault gun and tank destroyer in early 1943 as the SU-152, with the chassis of the KV-1S heavy tank as a basis. Although the resulting weapon (nicknamed "Zveroboy," or "Beast-Killer") proved effective at knocking out German fortifications around Stalingrad and heavy tanks at Kursk, the KV-1 tank it was based on was out of production due to inadequate armament, and the SU-152 was inadequately armored against enemy tank guns. When the new IS-2 heavy tank began production, the chassis was similarly modified to produce the much-improved ISU-152. Fielded at the start of 1944, 1,885 were produced before war's end, giving their best service in the urban battles at war's end. In addition to inheriting its predecessor's nickname, grateful infantrymen referred to it with the sentiment "Not pretty, but thanks!"
The ISU-152 fulfills three roles - heavy assault gun, mobile artillery, and tank destroyer - being very good at the first and adequate at the second and third. As an assault gun, it was typically escorted by infantry squads that would cover it from antitank teams while it used massive 43.5 kilogram explosive shells to demolish enemy bunkers and occupied buildings. On open ground, ISU-152s were generally placed in the second line of attack, several hundred meters behind advancing tanks, and could lay rolling barrages of high-explosive fire down ahead of an attack to shred enemy infantry lines. However, its medium range, slow firing rate, and low ammunition capacity make it less effective than a dedicated mobile artillery piece such as the German Wespe. As a tank destroyer, it is less effective than the lighter SU-100; although the 48 kilogram solid-shot AP shells it fired could end most German tanks through sheer mass the 152mm gun's low muzzle velocity and short barrel meant it was unlikely to hit a German Tiger or Panther before the latter could get off shots at the ISU-152. Nevertheless, the ISU-152's heavy armor forced even the heavy Tiger to come in to medium range and expose itself to escorting Soviet tanks. On the other hand, the massive high-explosive charge could kill even the Tiger from explosive shock damage, making German tank commanders rightfully fear the "Zveroboy."
Detailed Unit Info
In game, the ISU is your main anti tank force if you choose to go by the tank branch directly, as the t-70 and t-34 are not able to adequatly duel with most tanks at that stage. Although it's your only choice, it is terribly unreliable and needs constant managment, as there is no way of knowing if it will land a hit on the enemy or right in front of itself. Groups of ISU-152's have a tendancy to one shot allies, as any other tank lighter then itself unfortunate enough to be in the line of fire.
In most cases, you own't want the ISU to fire it's absurdly expensive shell at infantry, only to have to demonstrate the longest reload time in the game, so set it to return fire only, unless you're feeling rich.
Late game, the ISU-152 should be used in pairs to destroy heavier tanks like Tigers and IS-2's.