CAMD RF 38-11355-190
"NII #13 sent you a schematic of a 120 mm mortar to be installed in a T-34 tank. In the same letter, the Institute requests a T-34 tank to test the mortar in. Additionally, the Special Construction Bureau of the Uhtomsk factory requests blueprints of the T-34 and a T-34 tank to develop and test a 240 mm mortar for it.
Please respond with the decisions made and orders issued regarding these letters."
Yuri Pasholok further writes that the 120 mm mortar was to be placed in place of the F-34, using the same recoil mechanisms.
Another project involves a 152 mm mortar in the T-34.
CAMD RF 38-11355-190
"1. The 152 mm mortar in a T-34 is intended to combat enemy infantry, positioned behind cover, hardpoints, or ground-wood fortifications of the enemy.
2. Combat and tactical characteristics of the 152 mm mortar installed in a T-34:
a) maximum range: 1200 meters
b) minimum range: at most 300 meters
c) rate of fire: 2-3 RPM
d) number of charges: 1
3. The ammo rack must fit at least 25 shells.
4. The accuracy must provide the following groupings at 500-600 meters:
1) 1/100 forward and backward
2) 1/200 side to side
5. The artillery system must provide:
a) convenience during loading, aiming, firing, and unloading.
b) convenience during disassembly, assembly, and cleaning.
6. A maintenance kit must be developed for this system, as well as cases for it.
7. The aiming sight must be from an existing tank artillery system.
8. The sight must provide:
a) safety and convenience for the gunner.
b) reliability of its attachment and calibration during firing.
c) ability to aim the mortar in full rotation.
d) the ability to check your line of fire in field conditions without complicated devices.
9. In development of this system, use the following:
a) barrel with a breach and firing mechanism from the 152 mortar model 1931. The propellant charge must be recalculated to provide (with one charge) firing distances from 300 to 1200 meters.
b) anti-recoil mechanisms, and mechanisms of horizontal and vertical aiming currently used on the T-34.
c) use the existing shell from the 152 mm mortar.
10. The artillery system must be serviced by no more than two crew members."
The model 1931 mortar was previously used in the SU-5 SPG, but the T-26 chassis was deemed too weak for a gun of that caliber. It seems that the T-34 chassis was an answer to the artillery engineers' needs, but the only mass produced artillery piece to ever arise from that was the SU-122, an M-30 howitzer in a turretless hull.