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 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