SU-85 Requirements

"Tactical-technical requirements for a "tank destroyer" self propelled gun

1. Overall
1. The 85 mm SPG consists of a somewhat modified 85 mm tank gun on the modernized SU-35M chassis (SU-122M).
2. The 85 mm anti-tank SPG is designed to destroy enemy heavy tanks (90-120 mm of armour) at medium distances (500-1000 meters). In some cases, the gun can be used to destroy enemy pillboxes and armoured machinegun caps. 
3. The SPG needs to have good mobility and off-road performance, high mobility of fire, and excellent visibility of the battlefield.
2. Artillery requirements
1. The 85 mm anti-tank gun fires shells from the 85 mm model 1939 AA gun. In addition to this, a new HE-fragmentation shell will be designed (with the same ballistics) and subcaliber shells.
2. Gun characteristics:
1. Ballistics:
1. Caliber: 85 mm
2. Shell mass: 9.2 kg
3. Propellant mass (gunpowder 14/7): 2.48 kg
4. Muzzle velocity: 800 m/s
5. Maximum pressure: 2500 kg/cm^2
2. Design:
1. The barrel and chamber are the same as the model 1939 AA gun.
2. Vertical range: -5 to +25 degrees.
3. Horizontal range: +/-10 degrees.
4. Recoil length: 320-390 mm.
5. The mount and recoil mechanisms are the same as the 76 mm gun model 1941, with some modifications.
3. The 85 mm anti-tank gun must be similar to the tank gun (see requirements #2419) and only differ due to a lack of a coaxial machinegun.
   The design consists of an 85 mm AA gun barrel on the 76 mm ZiS-5 tank gun mount.
4. The overall design must have high compatibility of parts and assemblies with existing mass produced 76 mm tank guns and 122 mm D-11 howitzers, with some change in production tools.
5. The barrel should be a single piece, preferably without a muzzle brake. If a muzzle brake is used, use the stock breech. The breech is vertical, sliding, based on the 76 mm gun breech, with the same firing and semi-automatic mechanisms.
6. Rate of fire is 20 RPM, with practical rate of fire (including aim adjustments) of 10-12 RPM.
7. The hand trigger mechanism (no more than 8 kg of force) should be included in the elevation mechanism flywheel. Maintain the possibility of using a solenoid type electrical firing mechanism.
   Note: the use of mount and recoil mechanisms from the D-11 howitzer are allowed, the recoil length can be any value.
8. Aiming mechanism:
1. Elevation: use from the ZiS-5 (D-11)
2. Turning: screw type, with the speed of at least 0.75 degrees per wheel rotation, required force of 3 kg (from full stop).
9. The oscillating part of the gun should be naturally balanced.
10. The gun should be able to fire directly and indirectly. For this, a sight from the regimental cannon mod. 1927 and a telescopic sight are used.
3. Requirements from the chassis:
1. The modernized hull of the SU-122M (SU-35M) is used. Note: a secondary possibility is the use of captured PzIII and PzIV chassis.
2. The size and armour configuration are unchanged. The mass, due to the decreasing mass of the gun, should be 1-1.5 tons less.
3. The crew should be composed of 5: commander, driver, gunner, two loaders.
4. Install the following observation devices:
1. Commander: PTK and periscopic sight.
2. Other crewmen: periscopic sights.
   The total sum of observation ranges should result in good observation when stationary or in motion.
5. Dead zones should be no more than 5-7 meters, 3.5 meters for the driver.
6. External communication is done using a 9R radio, internal using a TPU-3F radio.
7. There should be a hatch in the roof for signal flags or rockets.
8. The following is kept in the fighting compartment:
1. 60 gun shells.
2. 1500 PPSh rounds.
3. 25 hand grenades.
4. 5 anti-tank grenades.
5. 2 PPSh
   A mixed ammunition rack is allowed, using horizontal and vertical placed shells.
9. Aside from ammunition and tools, the fighting and driving compartment should have room for a first aid kit, water and rations, the crew's personal belongings.
10. For self-defense, the SPG needs ports capable of fitting a PPSh. The dead zone of these ports should be no more than 10 meters.
11. Two hatches should exist for regular use by the crew: one for the commander and a two-part hatch in the top. An emergency hatch should be placed at the bottom of the hull.
12. There will be three types of parts kits:
1. Per-gun, carried with every SPG.
2. Per-battery, for 4 guns.
3. Per-regiment, for 12 guns.

Chief of the 16th department, Colonel Zhevanik

Assistant to the chief of the 16th department, Engineer-Major Solomonov

April 13th, 1943"

CAMD RF 81-12038-246