"To the Commander of the Motorized and Mechanized Forces of the Red Army, Marshal of the Armoured Forces, comrade Ya.N. Fedorenko
Having examined the results of comparative trials of the 122 mm D-25 gun and 100 mm D-10 gun, the Red Army GAU concludes that:
- The rate of fire of the D-10 gun is up to three times higher than that of the D-25 gun, which is a significant advantage of the D-10 gun.
The 100 mm D-10 gun presently has an insufficiently robust armour piercing shell, which does not guarantee reliable penetration of the Panther's armour at a range of over 1200 meters.
The decision to install the 100 mm D-10 gun on the IS tank should be delayed until the armour piercing shell and semi-automatic mechanism of the D-10 gun are perfected.
Since the 100 mm D-10 gun and its ammunition in its existing form are already significantly more powerful than the 85 mm D-5 gun, it is necessary to rearm the SU-85 SPG with the 100 mm D-10 gun, for which a pilot batch of SPGs with the D-10 gun should be produced with corrections of drawbacks of the gun and SPG that were revealed during trials.
- The 122 mm D-25 gun reliably penetrates the front armour of the Panther tank from a range of over 2000 meters.
The armour piercing shell of this gun is sufficiently robust, and the HE grenade has a sufficient explosion and fragmentation effect.
Until the ammunition and components of the D-10 gun are perfected, the 122 mm D-25 gun must remain as the main armament of the IS tank.
The mass and dimensions of a unified 122 mm round will make the loader's job more difficult, which will definitely not increase the rate of fire of the D-25 to the level of the D-10.
Regardless of the result of comparative trials of the D-10 and D-25 guns, the installation of the S-34 gun in a tank and an SPG will continue.
Commander of Artillery of the Red Army, Chief Marshal of Artillery, Voronov
Marshal of Artillery, Yakovlev
April 20th, 1944"
CAMD RF 38-11369-490 pp. 35-38