Unbuilt French cavalry vehicles of 1938-1942

[Elan Vital]

Hi everyone,

This thread will be dedicated to the discussion of French cavalry vehicles in the intended 1940-1942 period, namely:

- AM 39 Gendron-Somua
- Laffly heavy/powerful armored car
- Bucciali heavy/powerful armored car
- AMX-40 heavy/powerful armored car
- late Panhard AMD 178 derivatives
- Panhard AM 201 and AM 40P heavy/powerful armored car
- VPRC Bernard TT4 protected cavalry supply vehicle
- and possibly others...

Not the Somua S40 and derivatives, that will be for a thread I already created before.

Considering many of the entries here share a similar origin and historical context, I will start with that in the first post.

Context:

Prior to 1937, the armored cars had been divided into three categories:
- AMR: Automitrailleuse de Reconnaissance, lightly armed but mobile recon vehicles of very small size and weight.
- AMD: Automitrailleuse de Découverte, heavier scout cars with relatively heavy armament and meant to recon more deeply into the enemy lines.
- AMC: Automitrailleuse de Combat, a name chosen to circumvent the monopoly of the Infantry on the "Char" name, they were tanks in all but name.

All of these categories could accept either wheeled or tracked options. Other than the AMC class which grew to carry 20 to 25, 30 and finally 40mm of armor, all were only armored against rifle caliber bullets.

Things started changing in 1937 with an unsollicited proposal from Mr. Buccialli for a heavily armed and armored wheeled combat car. This grew into a February 1938 specification for a "powerful" armored car, initially meant to carry 40mm of armor and a 37mm SA38 gun within about 11 tonnes. This specification was amended numerous times, culminating at a 47mm (allegedly SA35) main armament and up to 60mm of armor basis, possibly as low as 9 tonnes.

This specification was tied to a progressive change in thinking within the French military, which was further vindicated by examination of the Polish campaign in 1939. It was concluded that simple bulletproof protection was no longer sufficient for a recon vehicle, hence the 40mm or 60mm of armor. It was also deemed that the entire AMR and AMD classes could be replaced with a single "AM" armored car embodying heavy armor and decent armament. The AMC designation had de facto been superseded by the designation of "Char". Vehicles developped for this specification were the Buccialli and Laffly armored cars, the former being deemed too risky and the latter too conservative. In the end, it is the innovative Panhard proposal which was selected, initially in a non-compliant configuration as the AM 40P.

As for the AM 39 Gendron-Somua, it was a late entry in the old AMR program which proved sufficiently interesting to warrant further development and a production order for 150 to be delivered starting from the second half of 1940. However, it was still doomed and was not meant to continue in production beyond that number. The AMD 178 was similarly doomed, as of mid-1940.​

 

[Elan Vital]

Let's start with one of the most obscure of them all, the AMX-40. This tank has so far eluded every single of my archive digging sessions, probably because tank-related archives tend to be split between cavalry and infantry (hence why I found little on the Somua as well) and my research de-facto often led to Infantry Branch-centric documents. I unfortunately do not expect to dig up anything about it anytime soon.

The only primary source so far is a digitized plan on the SHD's website Mémoire des Hommes, with the only other source being an interview from the AMX's lead engineer of the time, Joseph Molinié, long after the events (with all the limitations such late interviews can have).

History:

The history remains by far the most obscure part of this vehicle, as I have found no mention of it yet in any French Army report on ongoing studies. What has been gathered so far is that following an April 1939 French visit in the UK under command of the General Tank Inspector Martin, the French got to witness the recent A13 Mk I Cruiser Tank. The Christie suspension it used attracted significant interest, to the point where an A13 was apparently sent to France for study.

Fast forward to March 4, 1940, with AMX releasing a plan of a "Cavalry Tank" built around this style of suspension. It is alleged that this vehicle was meant as a potential replacement for the Somua cavalry tank and its conceptually ageing and complicated suspension.

It is not known if the project caught the interest of the Army. Without more plans from other times, it is difficult to assess where the project was in May 1940 or when it truly started.

Design:

The plan at least was quite detailed, giving us a good deal of insight into this rather innovative vehicle, which marked a major departure compared to previous AMX designs.

Layout and armor concept:

The AMX-40's layout and armor organisation differed considerably from previous AMX designs. Until then, they were built using rolled plate which was welded or bent with resulting angular designs, with only limited use of casting. Here, castings were widely used, leading to a very rounded shape.

The driver sat centrally at the front, between rows of machinegun drum magazines and with the batteries to his left. A large hatch above him contained three PPL episcopes. Unusually, the turret was operated by two crew members, a commander/gunner and a loader. The turret ring is alleged to be 900mm wide, which would be quite cramped, though in appearance the crew could still fit. The armament was composed of the ubiquitous 47mm SA35 gun and a coaxial 7.5mm MAC machinegun, with a +18°/-14° vertical traverse arc.

Firepower was enhanced through the use of a 1m base stereoscopic rangefinder with an observation head with a field of view of 50°, and a rangefinding head with a FOV of 15°, unique for this gun (usually this system was meant for long 47, 75 and 90mm guns). Finally, there was a panoramic periscope. 34 7.5mm MG magazines (4 in the turret and 30 in chain-driven conveyors on either side of the driver, for 5100 rounds) and 122 47mm rounds (only in the hull) were carried. There is finally an odd mounting for a AA machinegun behind the fighting compartment.

Unlike most other French turrets with an electric turret traverse mechanism, this one used a hydraulic system.
As usual, access to the turret was through a large 600mm-wide rear door.

The front part of the hull at least met a 60mm basis thickness, but many parts were steeply angled or likely thicker than necessary owing to French armor specifications to account for the orientation of the tank when moving. The rear was 40mm thick, the roof 20mm thick. The floor was curved in a V-shape, 25mm thick and well spaced from the fake floor, which should have ensured a good level of protection against AT mines (in comparison, the S40's belly was to be 20mm thick).
The sides were the most particular. The sponsons were spaced with 15mm vertical plates internally, then diesel or oil tanks for extra protection, and finally a very curved and angled section going from 50 to 30mm plate thickness.
The lower sides were 40mm thick internally, and spaced with side skirts which were 30mm thick over the upper run of the tracks, and 15mm thick below, likely assuming that the wheels would bring the protection to the same level.

As such, even assuming that the spaced arrangement would perform no better than the same mass of steel against full-bore projectiles, the entire front and sides of the vehicle at least met a 60mm basis level of protection, if not greater in many places. The turret itself was 60mm thick all-around. The use of fuel in the sponsons was quite novel for the time, allowing an efficient use of space and weight.

Suspension:

The suspension was built around 4 820mm-wide double wheels per side, sprung on long angled coilsprings much like the low-profile Christie suspension used on British Cruiser tanks from Covenanter/Crusader onwards. Contrary to British designs, the AMX proposal kept the last two wheels of each side powered and with chain drives to use on wheeled mode, mostly as an emergency measure in case a mine destroyed the tracks.

The suspension springs were also mounted externally, but were protected by side skirts, the lower part of which was removeable. Maintenance was thus somewhat easier, while retaining the benefit of some protecting for the suspension elements. In theory, this also reduced the amount of space "wasted" by an internal arrangement. The tracks and wheels were surprisingly only 260mm wide, with a ground contact length of 2940mm, which meant that at a weight of 16 tonnes, the ground pressure could reach 1.04 kg/cm², which is well in excess of Army requirements.

The primary merit of this suspension type over the types in use in France back then would be the reduced rolling resistance, reduced roadwheel speed and thus possibly wear, and greater wheel travel, all more conducive to a fast vehicle. The reduced number of parts (even if bigger) compared to the multi-small-wheel bogies of the S35 and co. also could reduce complexity.

The higher-placed front idler was naturally conducive to greater wall-climbing capability than the S35, but the S40 would have done better.

Automotives:

The powertrain was built around the Aster 4-cylinder 2-stroke diesel engine, a staple of AMX designs already seen on the AMX-38/39. Meant to deliver 160 PS at around 2000 rpm, it was a very close analogue to the Detroit Diesel 4-71.
Logically, the weight would have to be around 16 tonnes to meet the minimum 10 PS/t requirement of the Army, which AMX full well knew with the discussions around the AMX-38/39.

The engine was placed on the left side of the hull, with a large centrifugal fan, radiator, air filter, oil cooler and air piping system all placed on the right side. Behind the engine sat a Robin-Van Roggen (RVR) continuously variable gearbox and differential.

The RVR was a Belgian system in development since 1934 and experimented on Imperia cars, and was a style of automatic transmission which automatically moved the point of application of the engine's connecting rods. The war put a stop to its development.

Dimensions:

Length: 5330 mm
Height: 2370 or possibly up to 2450 mm (hull only without ground clearance 1225 mm, about 1050 mm above the fake floor)
Width: 2450 mm in total, 1320 mm inside the hull
Ground clearance: 400 mm

Observations and conclusion:

The AMX-40 was certainly a very progressive vehicle, featuring a suspension more conducive of fast movement, an excellent armor layout for the time, a progressive diesel engine, a rangefinder and an attempt at obtaining a 2-man 47mm SA35 turret.

Many zones of uncertainty remain. The mobility requirements would assume that the weight is at least below 16 tonnes, however, the tank retains most of the general dimensions of the Somua S35 while being larger and much more heavily armored (admittedly, the belly spacing means the actual side armor height is some 100mm lower, and the hull is a little shorter, while some of the width is due to the side skirts and suspension spacing). It is also generally bigger than either the AMX-39 and Renault DAC 1, the former reaching already 16.5 tonnes with thinner armor and the latter reaching 18/19 tonnes with 60mm-thick sides. Whether the tank actually could stay below 16 tonnes was thus very uncertain.
The tracks appear too narrow to meet the ground pressure requirements of the time.

It is not certain that the design itself would have kept this form even if it progressed to a production vehicle. The 1320mm fighting compartment width is a hard limit on the turret ring diameter and thus armament, which is already apparently cramped for 2 men, and while the 47mm SA35 could well have become marginal by 1941. The castings themselves might have been too complex for a WW2 tank. Any weight growth would require at least the 220-240 hp 6-cylinder Aster. In any case, without knowing more about the design or what the cavalry might even want of a future cavalry tank, it is hard to say.
​

 

[dan_inbox]

And here is a CGI render of this very rounded beast: