85 mm Vertical Stabilizer

"To the Chief of the 2nd Department of the GAU Artillery Committee, Major General of the Artillery Engineering Service, comrade Komarov

Acting Chief of the 1st Department of the GAU, Engineer-Colonel comrade Yakunin

RE: progress of work on the experimental ZIS-S-54 guns

I report that factory #112 finished the installation of 4 ZIS-S-54 guns with gyroscopic stabilizers in the turrets of T-34 tanks and that they are currently going through the final tuning process, checking of the gyroscope, hydraulic pump, power circuit, and other components of the gun stabilizer.

The last 5th gun is currently being installed in the turret of a tank.

I consider that the final tuning of the gyrostabilizer with the ZIS-S-54 gun in 5 experimental tanks and their trials, both mobility and gunnery, will be performed in July of 1945.

Preliminary comments regarding the ZIS-S-54 gun based on observation during installation:

1. The flexible shaft from the drive mechanism to the elevation mechanism has a lot of bends in it. A number of them (in the vertical plane) can be removed by turning the casing of the worm gear pair by 15-20 degrees.
2. The process of turning the gun elevation mechanism on and off is long and inconvenient due to an inconvenient position of the elevation mechanism switch. The switch is located underneath the gun elevation mechanism casing and is right up against the turret ring guard. The switch should be moved close to or right next to the elevation flywheel.

In addition, the center of gravity of the gun in the Y axis is lowered (the 112 kg gyroscope is placed under the recoil guard), which makes it necessary to weld a 350-450 kg counterweight above the gun mantlet, which in turn reduced the range of observation through the observation devices in the fighting compartment of the tank.

GAU KA military representative, Engineer-Major Zheleznyak

July 18th, 1945"

Via Padikovo museum.