Attempts to create fixed ammunition for the 122 mm D-25 gun in 1944-45
It is no secret that the firepower of tanks in WW2 increased dramatically. Armies of the world began the war wither with 37-47 mm long barrelled guns or 75-94 mm short ones. Some tanks even had armament composed only of heavy machine guns or small autocannons. Firepower of heavy tanks increased the most noticeably, particularly in 1943. German heavy tanks settled on the 88 mm caliber, the Americans focused on 90 mm guns with ballistics of the M3 AA gun. The USSR also initially chose an AA gun, an 85 mm one. However, there was a huge leap forward in the summer of 1943. The design bureau of factory #9 under the direction of F.F. Petrov developed the 122 mm D-25 gun by combining the D-2 122 mm gun (its ballistics were very close to those of the A-19) and the cradle of the 85 mm D-5T-85 gun. After trials in the Object 240 experimental tank, it was accepted into service as the IS-2 (IS-122) on October 31st 1943.
|The D-25T gun had no alternatives. There were many attempts to replace it, but Petrov's creation survived 3 generations of tanks. It was only replaced with the M-62 on the T-10M.
|100 mm guns were considered the most promising by the fall of 1943, but they were still in development as of February 1944. Malyshev placed his bet on the D-25T gun.
|Fixed ammunition for the D-25T-44. Surprisingly, this development was not reused a year later.
|The idea of using a D-25T gun with fixed ammunition on the T-44 was abandoned since the round was still too large and inconvenient. The ammunition capacity also became too small.
|The ISU-122S was the only vehicle where the rate of fire issue was resolved via the installation of the D-25 gun that was supposed to use fixed ammunition.
|Blueprints of the fixed round. The AP round was 1.2 meters long and the HE round nearly 1.4 meters.
|Two results of trials from the NIBT Proving Grounds (1, 2). While the situation with the ISU-122S was evaluated a bit pessimistically, the IS-2 could indeed only be loaded by an acrobat.
|This image illustrates the chance of success at trying to fit fixed ammunition into the IS-3 tank.
|There was no point in continuing the trials in November of 1945 since the ISU-122 was removed from service.
|The fix to the rate of fire problem on the T-10. A mechanical gun rammer was introduced to increase the rate of fire to acceptable levels.