Specification Crew : 4 Combat weight : 46,500 kg Max speed : road , 40 km/h Length : 9.85 m Width : 3.15 m Height : 2.45 m Main gun : 121.9 mm gun

The new "Kirovets-1" heavy tank project commenced in summer 1944. This project was undertaken after a detailed examination was performed of the types and locations of battle damage inflicted by German antitank weapons on Soviet armored vehicles. There were, in fact, two different heavy tank projects being developed under two competing engineering groups: one group led by J.Y. Kotin and A.S. Ermolaev, and the other group led by N.L. Dukhov and M.F. Baldji. The first project was based on Objects #244, #245, and #248. The main feature of this project was the unusual frontal armor (glacis). It consisted of two plates welded at an angle, which sloped down from the center on both sides. Designers called this feature a "pike's nose", while western sources call it simply a "Pike." All previous tanks had flat frontal armor built from a single plate. The old version had two crewmen at the front of the tank: the driver and the radio operator. By removing the radio operator's position, the driver could be relocated to the center. This allowed the tank designers to reconfigure the sides of the glacis, creating two sloping "cheek-bones." The sloping armor reduced the tank's weight and essentially strengthened the hull from the front. Moreover, it was hoped that the sloping geometry would withstand enemy fire better. The semi-automatic 122 mm main gun was fitted with a muzzle brake. The rate of fire was about two to three shots per minute. Like its predecessor, the IS-2, the IS-3 normally carried 28 shells: eighteen high-explosive fragmentation rounds, and ten armor-piercing rounds. This ammunition distribution suggests that infantry and other 'soft' targets were intended as the main targets for the IS-3. The IS-3 carried four internal steel fuel tanks with a total capacity of 450 litres. The fuel tanks sat in pairs on both sides of the engine. Furthermore, the IS-3 was equipped with four cylindrical external fuel tanks. These external fuel tanks each carried 90 litres, and were connected to the internal fuel tanks. The external fuel tanks were equipped with emergency release brackets in case of a fire or a sudden attack The hull of the IS-3 was welded as opposed to being cast, as most foundries were already occupied with the manufacture of turrets for the IS-2 and the T-34. At the same time, the latest advances in welding technology allowed for welded hulls of robust construction.