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IS-5 Object 248

In response to the appearance on the battlefield of German tanks Pz. Kpfw. VI "Tiger", People's Commissar of Armaments D.F. On April 13, 1943, Ustinov sent proposals to the State Defense Committee to strengthen anti-tank weapons. Among the most important were: the resumption of production of the 57-mm anti-tank gun ZIS-2, which was curtailed in 1941, the use of existing developments on the 85-mm anti-aircraft gun of the 1931/1937 model, the creation of new cumulative and subcaliber shells, as well as the possibility of creating a powerful 100 mm anti-tank gun. The last proposal was put forward by V.G. Grabin.

In the fall of 1943, TsAKB developed two models of 100 mm tank guns. One of them was a ZIS-6 cannon rearranged on a 100-mm gun with a modified sleeve catcher and a vertical guidance mechanism, and the second was a 100-mm S-34 tank gun. Based on the correspondence on the NKV, it can be assumed that one copy of such a gun in September passed a test shot from the carriage of the 152-mm ML-20 howitzer cannon.

The S-34 cannon arrived from factory # 92 to factory # 100 not on 20 February 1944, as envisaged by the plan, but only in early April 1944. The production of the new tower was also delayed. Unlike the IS-4 turret, it had an inverted armored mask, due to the need to place the gunner on the right. In addition to the three crew members, it was also planned to place a mechanical rammer of shots in the turret, and subsequently to install a sight stabilizer (they were not submitted for the first tests). As a result of all these refinements, the heavy tank IS-5 (the first with this name, "Object 248" ) with the S-34 cannon was manufactured by Plant No. 100 only in June 1944.

In the spring of 1944, the S-34 gun was tested in the KV-100 tank, which was a serial KV-85 tank with a 100 mm gun installed in the standard turret. Due to the fact that the KV chassis by that time was already considered obsolete (due to the appearance of a more advanced IS tank), work on the KV-100 was not successful.

The first joint tests of the IS-4 and IS-5 tanks revealed the design flaws of both guns - the design of the gun cradles was not strong enough, the recoil devices were crying. The guns were returned for revision, but the test range workers still liked the IS-5 with the Grabin cannon, which provided better working conditions for the gunner and loader.

From July 1 to July 6, 1944, the tanks were retested at the Gorokhovets GAU test range . Now more reliable operation of the mechanisms of the D-10T gun was noted. The S-34 cannon was "capricious" again, in addition, the breech of the gun, which was rolling back when fired, could have hit the tank commander, whose workplace should have been moved even further to the right.

In October 1944 , TsAKB once again finalized its product. A mock-up of a mechanical rammer was placed in the IS-5 turret (due to the tightness, it greatly impeded the loader's work). A sight, stabilized in the vertical plane, appeared. The tank commander's workplace was moved even further to the starboard side, and the cradle design was also refined. The ammunition load of the gun was increased to 35 shots, but according to the testers, it was not possible to use the six shots located in the front of the hull in a combat situation.

Finishing of the IS-4 and IS-5 continued almost until the end of 1944. The tests confirmed the significantly increased combat qualities of the tank. In terms of rate of fire, the IS-5 (5-8 rds / min) significantly surpassed all known heavy tanks, it had no equal in terms of shell penetration and firing accuracy on the move.

Plant No. 9 was able to master the 100-mm D-10 cannon in series by September 1944, the production of an armor-piercing 100-mm unitary projectile was started in November 1944, but the deployment of mass production of a heavy tank with a 100-mm cannon was then considered inexpedient due to the significant deterioration in the quality of the armor of German tanks, the effectiveness of the 122-mm guns in service with the IS tanks increased significantly. And in terms of high-explosive fragmentation action, the 122-mm projectile was significantly superior to the 100-mm, so the GKO decided to abandon the installation of 100-mm guns in heavy tanks, and the artillery designers were asked to develop a new projectile for the 122-mm D-25T gun with greater armor penetration. Such a projectile, an armor-piercing blunt-headed with a ballistic tip BR-471B, appeared in the spring of 1945, but began to enter the ammunition of heavy tanks almost after the war.