ph3s: That was truly amazing to see that beast fire-up and drive up onto the load carrier. There was so much of interest in that video that I have watched it three times already. I found this in Steven J. Zaloga & James Grandsen, Soviet Tanks and Combat Vehicles of World War Two.
"The ISU-122 and the ISU-152 were used by independent heavy mechanized gun regiments. They were earmarked primarily for use by the tank corps, and were kept in the second line of attack behind the tanks to provide long-range cover fire against heavy German tanks or strongpoints. Although nominally an artillery weapon, they were used almost exclusively in the direct fire role, and regiments were often raised on the basis of existing heavy tank regiments with tank rather than artillery training." The engine was rated at 600 hp and provided a road speed of 43 KPH (26.7 mph). The 45.5 ton ISU152 could travel 330 kilometers (205 miles) on roads and 120 kilometers (74.5 miles) cross-country. Dwight