is4

Work on the IS-4 prototype began in Chelyabinsk without an official order from the Armored and Mechanized Armored Command and without a government license. It was supposed to be a vehicle competitive to the IS-2, exceeding it in terms of basic combat indicators, and in the future to replace it. The IS-4 tank was created in 1944 in parallel with the IS-3 heavy tank and was supposed to be a counterbalance for the German heavy tank PzKpfw VI B Königstiger. The main constructor responsible for the project was Lew Trojanow. Works on the prototype marked Object 701 (ros.Orъект 701) [3] were financed from the factory's internal budget. In the summer of 1944, a wooden model of the tank was assembled. Then several prototypes were created:

Object 701-2 with a mass of 55.9 tons. In the first version, the main weapon of the tank was a S-34 gun 100 mm caliber with a barrel with a length of 47 calibers, without an exhaust brake [d]. Additional weaponry was a DT machine gun 7.62 mm. Two experimental vehicles were created, one of which was equipped with a 122 mm S-34-1 cannon with extended barrel and muzzle brake [2].
Object 701-5 with a mass of 58.5 t. The increase in mass resulted from thickened armor. The tank was armed with a 122 mm S-34P gun. The cannon had a cradle with S-34 and a barrel with A-19. The vehicle underwent attempts to shoot in the second half of 1944 [2].
Object 701-6 with a mass of 60 t arose as a result of the reconstruction of Object 701-5. The vehicle was armed with a 122-mm D-25T gun coupled with a 12.7 mm caliber DSzK wkm. For arming the tank was finally adopted only in 1947 in the version corresponding to the last prototype [2]