"Measures to increase the combat ability of the IS-122 tank
1. Turret and hull
1. A hull whose strength matches the armament may only be reached by replacing the clearly obsolete shape of the upper front plate. The front of the IS-122 must be shaped like the front of the T-34, with a 120 mm rolled armour plate (figure #11) within the limits of the tank's dimensions (figure #12).
Figure #11. Parallel cross-section of the front of the IS-122 tank hull.
Figure #12. Front of the altered IS tank hull.
The necessity of producing this type of front hull is confirmed by penetration tests of the front plates of the Panther tank with the German 88 mm gun from the Ferdinand SPG. The upper front plate of the Panther tank, 85 mm thick and sloped at 55 degrees, could be penetrated with armour piercing shells at 600 meters. The altered front of the IS-122 tank hull will be impenetrable by armour piecing shells from the 88 mm gun (Ferdinand SPG) at any distance.
The front of the turret should be 200 mm thick, turret sides 150 mm thick.
2. Increase in fuel storage, ammunition capacity, and crew comfort may be reached by increasing the width of the hull within the dimensions of the tank (figure #13).
Figure #13. Perpendicular cross-section of the IS-122 tank hull.
Due to obvious advantages of rolled armour over cast, the upper hull should be produced with rolled armour. By placing the sides at 45 degrees (instead of the current 15), the thickness of the plates could be reduced to 75 mm.
1. Due to the outlines disadvantages of the 122 mm gun (two-piece ammunition, screw breech), it is necessary to replace it with a smaller caliber gun of equivalent power (preferably 100 mm). "
- CAMD RF 38-11355-2369
A lot of these features were implemented in the model 1944 modernization, but not all. For example, the 100 mm gun projects never really got anywhere. Instead, the gun was equipped with a superior semi-automatic sliding breech, but kept the two-part ammunition.
One-part ammunition was definitely attempted.
CAMD RF 81-12038-697
"To the Chief of the GAU KA, Marshall of Artillery, comrade Yakovlev
Regarding the letter from GAU KA from May 12th, 1945 on the topic of order 940670ss, I report that as a result of GOKS decision #6863ss on November 4th, 1944, NKV factory #9 developed an experimental 122 mm D-25 gun that uses one-piece munitions, and sent it to the Kirov factory on May 21st, 1945, in order to be mounted in the IS tank
I don't envy whoever had to serve as the loader on that experimental tank. 122 mm ammunition is rather large.
T-44, first variant, with 122 mm gun, demonstrating the dimensions of the shell.
Here are models of the existing IS-122 (center) and proposed hulls, surrounding it. Neither was used, but the right one inspired the IS-6 hull shape.
CAMD RF 38-11355-2606
The diagram is a bit convoluted, but it makes a lot more sense with the labels:
"Diagram #2. Placement of 122 mm ammunition in the IS-122 tank.
- Thirteen armour piercing tracer shells in the turret bay.
- Fifteen high explosive fragmentation grenades in the turret bay.
- Three additional shells affixed with belts to the lids on the ammunition crates.
- Twenty six propellant casings in the fighting compartment, and two on the side of the turret.
- An additional placement of three casings with propellant placed as follows: one on the lid of the left ammunition crate, one in the front left corner of the hull, one in the right hull bay."