Sunday, 27 October 2013

S-41 122 mm Howitzer Project

CAMD RF 38-11369-106:

"Explanatory note for the 122 mm self propelled S-41 howitzer project.

1. Overall view

The 122 mm self-propelled howitzer is designed as a weapon that accompanies infantry and tank units, destroys pillboxes and fortifications with direct or indirect fire, and fights enemy tanks and artillery. 

The main objective of this project is to produce a self propelled gun, with explosive and armour piercing power of the 122 mm shell, combined with mobility of the T-34 tank, by the method of the S-41 122 mm howitzer, which uses shells and ballistics of the model 1938 122 mm howitzer, mount, recoil mechanisms, and many other components from the ZiS-5 tank gun, the breech from the S-3 gun, and the SU-122 SPG, with minor changes.

The gun is composed of a new cannon on a mount from the 76.2 mm ZiS-5 gun. The S-31 85 mm tank gun and S-18 85 mm SPG gun are constructed in the same way. The S-41 122 mm howitzer and S-18 85 mm gun are interchangeable in their installation, and the same parts are used to install both at Uralmash (non-moving armoured components, frame, etc).

Changes to the SU-122 SPG that enable it to use the S-18 gun also enable it to use the S-41 howitzer.

Due to the semi-automatic sliding breech, there is no need for a breech operator.

The ammunition rack placement is the same as on the SU-122. 

The remaining 4 crew members, radio equipment, optics, PPSh, chairs, and other equipment does not change. The ammunition capacity is 50 shells. The mass of the SPG is 30 tons (SU-122 - 30 tons). The SPG with its S-41 howitzer allows for practical rates of fire of 8-10 shots per minute (with aim correction).

The vertical gun range is -5 degrees to +20 degrees (allowing for range of 8.4 kilometers), and the horizontal range is +/- 10 degrees, which allows for sufficient manoeuvrability of fire.

The semi-automatic vertical sliding breech, compared to the M-30 howitzer, results in a howitzer that is easier to service, and allows for installation of a coaxial machinegun or cannon. The roof is raised by 100 mm to aid the loader. The T-10 sight allows direct fire, and the S-3 sight allows indirect fire. 

The self propelled S-41 122 mm howitzer will have the same armoured hull and installation components as the S-18 85 mm self propelled gun. Overall, the S-41 project satisfies the technical-tactical requirements of the Red Army GAU for 122 mm self-propelled howitzers. 

2. Installation of the 122 mm S-41 howitzer in the KV-1S and IS-1 tanks

The design of the 122 mm S-41 howitzer and 85 mm S-31 gun allows for installation in the turrets of the KV-1S and IS-1 tanks using their existing turret rings, with the conversion specifics identical for both guns, as defined by the S-31 project.

KV-1S with 122 mm S-41 howitzer

KV-1S with 85 mm S-31 gun

The installation of a 122 mm howitzer in a tank provides a powerful weapon, capable of destroying pillboxes, fortifications, and combat all types of tanks and self propelled guns of the enemy, his artillery, and personnel. 

This is achieved by the large explosive power of the shell, its weight (23 kg), and muzzle velocity (515 m/s). 

The dimensions of the turret, placement of crew members, fighting compartment layout, turret basket, equipment, communications, optics, radio, seats, hatches, and other components do not change between the S-41 and S-31. 

In this case, the tank can carry 60 shells, 12 of them in the rear compartment of the turret, 10 on the turret basket, and the rest immobile on the fighting compartment floor. 

With a semi-automatic breech and one loader, the practical rate of fire can be as high as 5-6 RPM. 

The mass of the KV-1S with a 122 mm S-41 howitzer will be ____ kg higher than the mass of the KV-1S with the 76.2 mm ZiS-5 gun (43.5 tons), and will be equal to ____ tons.

The specifications of installing the 85 mm gun in the KV-1S and IS-1, and the changes made to the turret and fighting compartment also apply to the 122 mm howitzer (see the TsAKB S-31 project).

In conclusion, the 122 mm howitzer installed in a tank will solve the problem of arming the tank forces with powerful howitzers.

Table of data for the 122 mm S-41 howitzer project


S-41 Project

Gun caliber, mm



Muzzle velocity, m/s



Shell mass, kg



Explosive filler, kg



Propellant density



Maximum pressure, kg/cm^2



Chamber volume, dm^3



Full barrel length


Length of the rifled barrel, m



Number of grooves



Length of grooves



Mass of the propellant with casing



Muzzle energy, t.m.



Mass of the recoil mechanism

1000 kg

Recoil mechanism


Return gear


Recoil length

520 +/- 50 mm

Recoil resistance, tons


Mass of the oscillating part, without armour

1800 kg

Maximum elevation


Minimum depression



Force for vertical aiming

7 kg

Bore axis height



Roof height



Maximum height






Fighting compartment height



Distance from breech to ceiling




Same as SU-122




Practical ROF with fire correction



Ammunition capacity



Same as SU-122

Armouring of the recoil mechanisms

Same as ZiS-5

Overall mass






Table of data for the 122 mm S-41 howitzer as installed in the KV-1S tank



Bore axis height


Maximum height




Same as KV-1S

Height of the fighting compartment


Height from bore axis to ceiling


Turret ring diameter (projected)


Same as KV-1S

Practical rate of fire

5-6 RPM

Size of ammunition rack


Turret armour

Same as KV-1S

Overall mass

Composition of the 122 mm S-41 howitzer
  1. Barrel
  2. Breech (from S-3)
  3. Recoil brake
  4. Return gear (from F-34)
  5. Mount (from ZiS-5)
  6. Firing mechanism (F-34)
  7. Shell catcher
  8. Sight elevation mechanism (S-18)
  9. Elevation mechanism (F-34)
1. Barrel

The barrel monoblock consists of the following main components: barrel, breech, breech ring, buffer tube, and muzzle brake. The overall assembly is similar to the F-34 monoblock, with the difference that instead of two buffer tubes, there is one and a muzzle brake. 

2. Breech

It is a vertical sliding breech of the semi-automatic type, analogous to the F-34 tank gun breech. The use of a sliding breech, compared to the M-30 screw breech, makes the operation of the gun in a turret much more convenient, increases the rate of fire to 8 RPM, and allows for a coaxial machine gun or cannon.

The improved breech removes the necessity of a special loading tray. The sliding breech is much cheaper and simpler to manufacture than a screw breech. 

3. Recoil brake

A spindle type hydraulic brake, same as the one used by the F-34, with the following components replaced: stem, spindle, regulator ring, stem head, stem head nut, and centralizing ring. The replacement of these parts is caused by the increased ballistics and recoil length, and improvement of the robustness of some parts due to the heavier load on the recoil brake.

4. Shell catcher

The shell catcher is a U-shaped bent pipe, filling the role of a recoil guard. A sack is hung up on the pipe to catch shells.

5. Elevation mechanism

The elevation mechanism is from the F-34, with the exception of the flywheel, which is increased in size from 65 mm to 105 mm, with the goal of easing the force applied to rotate it.

6. Return gear

Identical to the F-34.

7. Sight elevation mechanism

The tank version of the mechanism is identical to the ZiS-5 mechanism, the SPG version of the mechanism is identical to the S-18 mechanism.

8. Mount

ZiS-5 mount with several changes.

Chief and Chief Engineer of the NKV TsaKB, Lieutenant-General of the Technical Forces, Grabin

May 27th, 1943"


  1. This reads almost like a teleshop offer. :D
    "The all new S-41, now with 40% more boom. We all know you like (bunch of guns) so we made this Frankensteinian monster that can be asembled from the parts available of the shelf. NO need for retooling required"
    On the other hand it is a pitch to mount his gun in SU-122, IS and KV-1S.

    Oh now that I remember, what naming convention Soviets used when naming the guns. This one is S-something, others that I saw were ZiS-something, D-something and so on. Were these factory/beaurou specifications, or maybe do they define the use/role of the guns?

    1. S is TsAKB's project, ZiS is Stalin Factory, D is factory #9. I'll post a partial list of the codes one of these days.

    2. Does this mean that the ZiS S-53 was a joint project then?

    3. Wikipedia states that S comes from the name of the engineer that adapted the ZiS-53 so it could be placed in T-34/85 turret.