Somua S35 unbuilt variants

[Elan Vital]

Hi everyone,

This thread will be about unbuilt variants of the Somua S35 family, in the same vein as my previous thread about Keller program vehicles, based in part on my research at the Vincennes archives.

This will include (as of current knowledge):
- Somua S40
- Somua S40 with FCM multi-man turrets
- SARL 42
- Somua SAu 40
- other Somua S35-based SPGs.

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I will be starting with the FCM turret projects for a modified Somua S40.

Work on these projects is explained in a descriptive note from the 24th of April 1942 from the FCM (Mediterranean Foundries and Shipyards), based notably in Marseille. Here is a translation of the note:

A - Project of 2-man turret with 47mm SA 35 gun.

1°) Mandatory conditions

- Turret ring of 1505mm (ball center distance), fitting within a 1490/1605mm wide hole
- Electric and manual traverse mechanism
- Turret body armored at 40mm on all plates but the roof and floor which are 20mm thick.
- Armament: 1 47mm SA 35 gun with a coaxial 7.5mm machinegun
- AA armament: twin 7.5mm machineguns with increased rate of fire (author's note: analogous to the aircraft MAC 34 M39 machineguns)
- Crew: 2 men: 1 commander with an observation cupola located on the right of the guns with a hatch to observe directly outside, and a gunner located on the left.
- Communication means: radio, signal flags and openings

2°) Description

The turret body is made of rolled armor plates, bent and assembled with joint covers or welding.
The mantlet and the cupola are made of rolled, stamped and welded plates.
The turret body is mounted on a turret ring placed in an opening of the tank's roof.
Turret traverse is done with a manual mechanism or an electric motor.
The controls are doubled so that both the gunner and commander can traverse the turret.
The armament is composed of a 47mm SA35 gun coupled with a coaxial 7.5mm MAC 34 machinegun with a firerate reducer which brings the ROF back down to 600 rpm.
The main gun can be shot with a manual or electric trigger.
AA defense is done by the tank commander who has a twin mount of MAC 34 machineguns firing at 1200rpm each. Elevation angles are from 0 to 80° above the horizontal plane.

The means of observation are as follows:
- for the commander: 3 PPL episcopes with a total forward field of view of 180°, 4 vision slits, one aiming sight and one target designation sight.
- For the gunner: 1 Gundlach periscope, 2 vision slits and one aiming sight.

20 rounds of 47mm ammunition and 15 MG magazines are stored in the turret itself.
Good comfort is ensured by a turret basket in which access to the different observation levels is obtained by adjustable floors.
The turret can be accessed from inside the tank and from the observation hatch on the roof.

The weight of the turret without the basket and ammunition is roughly 3800kg.

B - Project of a 3-man turret with 47mm SA37 gun.

The first project can mount a 47mm SA37 gun instead of the SA35 gun. In this case, proper servicing of the weapon requires a 3-man crew: 1 commander designating targets and ensuring continuity of observation, one gunner and one loader.

The project has been established to fulfill these requirements without modification of the turret basket and traverse mechanism..
The commander and gunner are located on the left of the weapons which are moved slightly further right.
The loader is on the right of the weapons.
The weight of this turret is similar to that of the 2-man turret.

The pictures of the turret are the first accessible in Part 1 of my Vincennes archives album:

Les Archives de Vincennes

2052 new items · Album by Alexis Michel

photos.app.goo.gl

Sadly, this was my very first visit there so the quality on those was less than stellar. Higher quality ones are in spoilers

Spoiler: Turret plans

My observations on the plans:
- the 3-man SA37 turret carried 24 ready rounds rather than 20.
- the AA twin MG mount was stored inside the turret near the cupola's hatch, with a mechanism to lift it over the hatch.
- the 2-man turret is 1870mm long, 1670mm wide, and 865mm tall (a little taller than the APX-1 CE on S35 and early S40).
- the inside diameter of the turret ring, so the real diameter accessible to the crew, was 1435mm or 56.5 inches, so a little bigger than/comparable to the T-34-76 and many British tanks of the time with a turret ring diameter of 54 inches.
- a complete revolution of the turret could be done in 20s (18°/s) with the electric motor, 1min20s with the manual mechanism.
- complete weight with the aluminium turret basket and ammunition was 4373 kg. In comparison the APX 1 CE weighed 2000-2200kg fully loaded (not sure if everything is included), so in the most pessimistic esimate the turret would have added 2.2 tonnes to the weight of the S40, notwithstanding the weight increase/reduction caused by modifications to the hull.

It is not known what modifications would be needed on the S40's hull to accept the larger turret ring, nor what modifications were contemplated unrelated to the new turret itself. However, the location of the radio in the turret all but guarantees that the radioman located in the hull of the S35/40 would be removed in favor of...something else.
This project had been apparently done in the context of restarting production of the Somua S40 in Vichy France for the Axis in 1942. Nothing came of this until the invasion and occupation of this part of the country after November 1942.

Overall, the FCM turret project was a natural follow-on to the projects that had been undergoing since before the Fall of France for turrets using welded and bent rolled plates rather than castings, and fixed observation cupolas instead of small rotating cupolas like the cast APX turrets. Both FCM and ARL (the latter with patents and major contribution from the Five-Lilles steelworks) had been designing 1-man turrets to replace the APX-1/4 cast turrets, with introduction starting in July 1940.

It was claimed by a well-known French historian, Stéphane Ferrard, that work on such a type of 3-man turret had started at FCM in April 1940, but to this date I cannot confirm this claim.

It is interesting to note that, unrelated to this program, a report on the lessons of the battle of France and on the creation of a new armored division written in 1940/41 envisionned the use of Somua derivatives with a 2/3-man 47mm turret and a 75mm turret, which are eerily similar to this project and the clandestine SARL 42. It is quite possible that thinking from armored officers inspired these programs or that this simply was convergent evolution.

Regardless, the FCM project was a logical way of using the limited French tank production capabilities which may have been accessible to France in the case of a program approved by the Axis authorities or launched after a very early liberation of France. It allowed the use of a well-known chassis that would be easier to put back in production, while adressing many of the problems of the Somua: it brought one or even 2 crew members in the turret, improved observation capabilities, added a more practical access hatch and more ready ammunition and greatly improved antitank capability in the case of the 3-man turret (to the level of a Pz III with a 5cm L60 gun).

This tank would obviously have been obsolescent from day one by the standards of major powers even if it could enter production in 1943, as it retained now very thin 40mm armor, and modest level of mobility (potentially fast, but only around 10 hp/t). Nonetheless, for non-German Axis powers and co-belligerents like Italy, Hungary or Romania, it was better than nothing and could even compete with a lot of their designs, like the M15/42 which was no better armored, nor more mobile, and more poorly armed, or the Turan I/II which also had poorer antitank capability and barely better armor and mobility. Whether this could have been an actual net gain for the Axis considering their production capability and ressources is however very uncertain.

 

[Elan Vital]

In November 1935, the SOMUA offered a few SPG projects based on the SOMUA AC3 chassis (S35 prototype), long before the more well-known SOMUA SAu40 (also called CAM 2 or AC4).

Here is a translation of the offer:

Mister General Inspector,

We have the honor of sending you hereby attached, a preliminary project for a self-propelled field gun obtained by installing a 75mm Schneider 12 or 14km gun on the fast tank SOMUA AC3.
As we explained on the "General" section of the associated note, this preliminary study has been established in order to set the rough lines of a self-propelled field gun featuring an armament of the greatest power compatible with the space available on the SOMUA AC3 fast tank prototype.
The envisionned solution allows the combination of firepower, tactical and strategic mobility, quick deployment, offroad capability and sufficient protection to not fear infantry projectiles or schrapnel.
This solution, built on the principle of the integral use of a proven vehicle and of existing and proven weapons, gives the advantage of envisioning an eventual realization which would present the minimum of risk.

Translation of the note:

Such a realization would lead to a type of equipment which could be logically used as the element of self-propelled batteries. This materiel used alone (commented: No) could also be an excellent infantry support asset.
The gun used is a powerful 75mm Schneider, firing a 6.5kg explosive shell at a muzzle velocity of 715 m/s, providing a range of 14km.

The ammunition capacity of this equipment could be at least 76 rounds stored as indicated on the attached project.
Servicing of the vehicle could be done by 3 crew members:
1. A driver sitting on the left
2. A gunner sitting on the right.
3. A loader standing on the right
Eventually, a 4th standing crew member could also be in the fighting compartment to work as second loader or radioman.

Summary Description

The cavalry armored car SOMUA which we suggest to turn into a self-propelled piece is composed of:
1. A rear section exclusively dedicated to the engine, transmission and controls of the tracked running gear.
2. A front section called "fighting compartment" in which everything regarding the armament with ammo and personnel and the driving compartment are organised and gathered.

The oscillating mass includes:
1. The gun with its muzzle brake and vertical wedge breech.
2. The housing for the hydraulic brake with counter-rod and the hydro-pneumatic recuperator.
3. The chassis on which the housing slides during recoil, holds the brake and recuperator attachments, the trunions and the mobile mantlet and the vertical traverse gear
4. The automatic breech opening and closing mechanism.

(Rest is just typical carriage and gun control suff):

Vertical traverse range is -5 to 45°
Horizontal traverse range is +-5°

The aiming equipment is a monobloc assembly located on the right trunion containing: an elevation cam, an elevation goniometer, an elevation mechanism and a x4 panoramic goniometer. This device allows direct and indirect fire.

When moving, the oscillating mass is locked at an angle of 30° and recoiled the maximum recoil distance (1.2m) inside the tank.

The fighting compartment is ventilated by the engine fan. There is a small hatch to dispose of spent cases, and ammo racks possess an evacuation device for gases.
Side access doors are available.

Ballistic data:

Calibre	75 mm	75 mm
Muzzle velocity	715 m/s	600 m/s
Projectile weight	6.5 kg	6.5 kg
Weight of complete round	9.5 kg	9.5 kg
Maximum range	14 km	12 km
Ammo capacity	76	76
Weight of ammo	700 kg	700 kg

Length of the barrel	3150 mm	2820 mm
Number of calibre lengths	42	37.6
Firing height above ground	1430 mm	1430mm
Above floor	1000 mm	1000 mm
Elevation angle	-5/+45°	-5/+45°
Traverse angle	5° either side	5° either side
Recoil force (horizontal)	3790 kg	2560 kg
Recoil distance	1200 mm	1200 mm
Weight of oscillating mass	658 kg	605 kg
Weight of the artillery piece (roughly)	1000 kg	950 kg

The final weight of the SPGs will be determined at a later date dependent on the armor thickness and width that will be approved after a more thorough study.
However we can estimate that the total weight of this vehicle will be on the order of the SOMUA AC3 with an APX1 turret (20 tonnes).

Translation of the reply from December 1935:

The general organisation of this materiel presents the following major defects:

1. The tank is blind

The only observation equipment is a panoramic sight fixed on the carriage and whose method of employment would only make sense if the vertical walls of the fighting compartment were deleted.
To use this panoramic sight, one would have to lengthen the sight body so that it emerges on the roof; but the disposition envisionned by the SOMUA seems to be hardly suitable for this organisation.

2. No tank commander is intended

The driver being the only crew member with good view of the exterior, it seems impossible to give command of the tank to another crew member. I also add that it seems pretty much impossible to direct the movement of the tank under enemy fire without having all-around vision.

3. The artillery piece is poorly protected.

The chassis and tray of the gun stick out of the armor but are too fragile to be exposed to enemy fire without special protection. It will be necessary to protect these elements with armor which would increase the weight of the oscillating mass.
Moreover, when moving, the forward part of the hull extends beyond the idlers. Is it to be feared that the hull, when moving offroad, would dig into the ground much like happened on numerous occasions with the first 75mm SPG studied by Général GARNIER.

4. The equilibrator of the oscillating mass will not work.

While it is possible to balance a field gun with springs as the joint is mostly vertical, this solution is not acceptable for a tank able to fire in any position, especially when the seating plane can be 15° away from the horizontal plane. The greater this unbalance, the more serious the drawback.

5. The ball joint of the gun is of excessive dimensions.

A ball joint of such size presents the following drawbacks:
a) it makes sealing of the joint difficult
b) it gives a large attack area, and thus increases enemy hit probability on the trunions and aiming equipment
c) reinforcing the ball joint armor may increase unbalance of the gun and make the work of the equilibrators worse

6. The organisation of the aiming sequence is not rational

The gunner is a separate crew member from the driver. It is to be feared that the gun will never be aimed roughly where the target is. (Author's note: this might be why the driver was the main gunner on French casemate guns of the time like the B1 and ARL V 39 SPG. One can obviously question this assessment considering that workable WW2 SPGs had a separate gunner).

In these conditions, I consider this project of no interest.

Plans of these vehicles can be found on 2nd part of my archive album here, relatively early:

Les archives de Vincennes Partie 2

1511 new items added to shared album

photos.app.goo.gl

The project that was discussed here is better-known as the SOMUA CAM 1:

There is another SOMUA SPG plan here which is somewhat different as it features a more normal mantlet with -10/+20° elevation and a machinegun turret. It also retains the weird front roller that was on the AC3 prototype and previous SOMUA vehicles.


Overall, a fairly flawed but imaginative initial project. The rather high elevation angle and big ball joint was likely intended to provide best conditions for dual use in the direct and indirect role, as HE throwing seems to have been the main intended mission rather than anti-tank duties.
The most interesting aspect remains the sheer power of the envisionned weapon. The 75mm Schneider 14km (based on an AA gun following the 75mm mle.1928 ballistics) eventually became the basis for the ballistics of the clandestine/postwar 75mm SA 44 gun, and was an intermediate between the typical medium 75mm (Sherman, T-34) and the medium-high velocity 75mm (KwK 40 L/48). The Schneider 12km was a more modest type roughly close to the gun of the Sherman.