"In order to make loading of the S-31 tank gun in the KV-1S and IS-1 tanks comfortable, the following must be done:
- Increase the distance from the bore axis to the roof to 470 mm (280 mm on the IS-1) as ramming an 85 mm shell at face height is difficult and impossible if the gun is depressed.
On most modern foreign heavy tanks and on our SPGs the space between the bore axis and the roof ranges from 400 to 500 mm.
Raising the roof over the loader will result in a small increase in the size of the turret, but it should not significantly impact the vision from the commander's cupola that is now being developed if it is placed correctly. - The loader must be able to work while standing, for which the height from the floor to the ceiling needs to at least 1650 mm.
- A rotating platform attached to the turret with a rack for 13 rounds of ammunition is needed to make the loader independent of the turret rotation. This exists on the T-6, Sherman, Churchill, and other tanks.
- To give the loader 15-18 rounds in a ready rack, the turret bustle must be enlarged. This will also balance the turret and make it easier to traverse, especially on the move.
- Make the ammunition racks, especially the one next to the loader, quick to use, comfortable, compact, and well polished in every detail.
All of the above requirements apply both to the KV-1S and IS-1 tanks.
The existing KV-1S turret can be used for both tanks after certain changes to raise the roof above the loader and enlarge the turret bustle. It is not to be changed in any other way (size, design, equipment).
The resulting tank with an S-31 gun will have an aimed rate of fire of 8 RPM and on the order of 12-15 RPM without correcting fire.
The ammunition capacity is set at 70-71 rounds for the IS-1 tank and up to 754 rounds in the KV-1S tank. In total, the installation of the new 85 mm S-31 gun instead of the ZIS-5, including the increased weight of the ammunition and turret, will increase the weight of the tank by about 2 tons in total."
