"To comrade L.P. Beria
On installing the 100 mm D-10 gun produced by NKV factory #9 into the IS tank instead of the D-25 122 mm gun made by the same factory
In March of this year, I reported to you that NKTP factory #100 jointly with NKV factory #9 produced an experimental prototype of the IS heavy tank with a D-10 gun designed by factory #9.
Trials of the IS with a 100 mm gun showed that the 100 mm D-10 gun has undeniable advantages over the 122 mm D-25 gun as armament of the IS tank. These advantages are as follows:
- The aimed rate of fire of the 100 mm D-10 gun in the IS tank is up to 8 RPM (on average 6 RPM), 2-3 times higher than with the 122 mm D-25 gun.This high rate of fire decisively improves the combat capabilities of the IS tank.
- A lack of a muzzle brake on the 100 mm gun improves the firing conditions for the crew in comparison to the 122 mm D-25 gun, which has a muzzle brake.
- The 100 mm D-10 gun weighs 300-400 kg less than the 122 mm D-25 gun.
- The dimensions of the parts of the gun that are housed inside the turret are less for the 100 mm D-10 gun than the 122 mm D-25 gun, making servicing the gun easier.
- The one piece round of the 100 mm gun is safer from the point of view of explosions and fires than the separate propellant of the 122 mm gun.
- The armour penetration of the 100 mm D-10 gun is greater, however slightly, than that of the 122 mm D-25 gun at ranges of up to 1000 meters.The 100 mm D-10 gun can penetrate the armour of all known tanks at a range of 2 kilometers, except for the front armour of the Panther tank and Ferdinand SPG.
Considering that factory #9 managed to create a 100 mm gun based on a family of guns already in service (85 mm D-5, 122 mm D-25) and that does not require serious changes to the design of the IS tank, I consider that it will not be difficult or time consuming to begin production of the 100 mm D-10 gun at factory #9 (instead of the 122 mm D-25 gun) and installation of this gun in the IS tank at the Kirov factory.
Considering the above, I consider it imperative to begin producing IS tanks with the 100 mm D-10 gun in place of the 122 mm D-25 gun.
If you are in agreement, I ask you to task the People's Commissariat of Tank Production and the People's Commissariat of Armament to prepare a draft GKO decree on this issue.
April 25th, 1944"