Categories
Cold War French Prototypes

AMX Chasseur de char de 90 mm (1946)

France (1946)
Tank Destroyer – None Built

Introduction

Following the liberation of the country in 1944 and the recovery of factories and design bureaus previously involved in the manufacture of armored vehicles, France immediately restarted studies of modern military equipment, with the intention of catching up to the other belligerents of WW2.

The Ateliers de construction d’Issy-les-Moulineaux, or AMX, formed in 1936 after the nationalization of Renault’s facilities in the same place, were a major contributor to this initial post-war rearmament effort. Their most well-known designs of the era were the AMX M4 (the future AMX 50) medium tank and 120mm Auto-Canon (eventually known as the AMX 50 Foch) self-propelled guns.

One of the more obscure AMX projects of the period, the Chasseur de Char de 90mm or AMX CdC, recently resurfaced with its introduction in the popular video game World of Tanks.

The Chasseur de Char de 90 mm, as depicted in the plan of June 5, 1946.
Source: Mémoire des Hommes

The sole source of information regarding this tank are four plans released between January 5 and June 26, 1946, developed by Favier, an engineer at AMX. These are now stored in the archives at Chatellerault and numerized and displayed in the database Mémoire des Hommes (Men’s Memory in English) of the French Defense Ministry. The “NOM 141” mentioned on the plans, as well as the presence of components common to the AMX M4, such as the gun and powertrain, indicate that the Chasseur de Char de 90 mm was developed under the same program, but as a dedicated tank destroyer derivative.

Overall Characteristics and Layout

The CdC’s design philosophy particularly stands out compared to its medium tank and SPG brethren. While the latter two were designed for protection against the medium and heavy caliber guns of the time respectively, the CdC could only hope to withstand light autocannon and small arms fire. The layout of its powertrain and suspension was substantially altered to reduce the overall profile. This resulted in a smaller and considerably lighter vehicle.

The hull was 7.38 m long and 3.25 m wide. The height to the top of the cupola was 2.78 m, and the height to the turret roof was about 10 cm less. The CdC was relatively low compared to the Tiger II and AMX M4, both of which had a similar main armament and were about 3 m tall. The vehicle weighed 30 tonnes empty and 34 fully loaded, over 15 tonnes lighter than the AMX M4 and 120 mm SPG.

The full plan and layout of the Chasseur de Char de 90 mm of June 5, 1946.
Source: Mémoire des Hommes

The vehicle otherwise retained a mostly conventional layout. The engine, transmission, and steering elements were located at the rear of the hull. The driver sat at the front left, with an ammunition rack, machine gun magazines, and batteries to his right. His hatch was located directly in front of him, in the upper plate. The turret housed a 90 mm Schneider SA45 gun, with the gunner to its left and loader to its right. The commander sat behind the gunner and had access to a small cupola with vision slits, but no hatch. The radio was located next to the gunner and its antenna was behind the cupola. The bustle housed an additional ammunition rack, and two doors were located on either side of it at the rear to allow entry and exit out of the vehicle. This was similar to pre-war practice, with a hatch at the rear of the turret, but was rather inconvenient on the CdC, as the hatches were far behind the crew instead of being close on the roof. A travel lock for the gun was installed at the very rear of the vehicle.

The plan of June 26 showed a slightly different layout, with an automatic loading and ejection system in place of the loader. It is likely that this crew member was deleted in this configuration, but it is not confirmed.

Armament and Ammunition

The tank was built around the massive 90 mm Schneider SA45 rifled gun. This was initially designed for the ARL 44 stopgap heavy tank as a response to the German 88 mm KwK 43 L71 gun of the Tiger II, which was encountered in France in 1944. It mated a new 5.85 m long (L65) barrel to the breech of the pre-war Schneider CA Mle.39S 90 mm anti-aircraft gun. The total length with the muzzle brake and the breech was 6.530m. The barrel was monobloc and autofrettaged. The breech was of the horizontal sliding type and was semi-automatically operated, meaning that the force of the recoil would open it after the first shot. It also had a compressed air scavenging system to evacuate propellant gases.

The oscillating mass was 3,150 kg and the recoil mass was 2,200 kg. The gun used a hydropneumatic recuperator and hydraulic recoil mechanism in the ARL-44, with a relatively long maximum recoil length of 700 mm. The recoil mechanism and actual length could have been different in the AMX CdC. As mounted in the AMX CdC, the SA45 had an elevation of +20° and a depression of -10° across the 360° range of rotation of the turret, which was excellent.

This gun could shoot a 10.6 kg APCBC shell (Obus de Rupture) (Armor Piercing Capped Ballistic Capped) at 1,000 m/s (11.2 kg when using steel instead of magnesium in the ballistic cap), or a prospective 8.5 kg tungsten-cored subcaliber shell at 1,130 m/s, as well as a 11.3 kg high-explosive (HE) round at 700 m/s. Its components were capable of withstanding operating pressures of up to 300 MPa. Using the APCBC projectile, it was considered comparable to the long 88s full caliber round or the Panther’s long 75 mm APCR (Armor Piercing Composite Rigid).

The ammunition was single-piece. The cartridge was 752 mm long and its rim diameter was 144 mm. The total length was 1,126 mm for the APCBC round, and 1,161 mm for the HE. For reference, the Tiger II’s 88 mm used ammunition with cartridge dimensions of 822 and 145-146 mm respectively, and near-identical full round lengths. The weight of the AP shells was almost identical, but the 90 mm HE was nearly 2 kg heavier, possibly with a greater payload. As such, the 90 mm was almost identical to the 88 mm in performance and ergonomics without being a direct copy. However, this meant that it shared the same drawback of very long rounds that were difficult to handle in the tight confines of the crew compartment. It also meant that the tank still had to be quite big.

This gun was undoubtedly on the higher end of Western tank armament of the time, reaching greater kinetic energy with AP (Armor Piercing) rounds than the 90 mm and 20 pdr armaments of American and British medium tanks, being surpassed only by 105 and 120 mm guns at the time being tested on the T29 and T34 heavy tanks and the French 120 mm gun then proposed for the self-propelled gun derivative of the AMX M4. However, the AMX M4 medium tank carried the same 90 mm piece, so firepower was not the outstanding feature of the tank destroyer.

The SA45 suffered heavily from the poor state of the early post-war French industry, with many defects encountered during production and testing of the ARL-44. The mechanical properties (rupture and elastic limits, elongation) of the barrel were also relatively poor compared to later production guns, such as the 75 mm SA50, limiting tube life relative to the operating pressure, and thus, the overall longevity of this armament. Its old technology led to excessive weight by post-war standards. By the early 1950s, even more powerful guns, such as the 100 mm SA47 and a 120 mm gun, superseded it in the AMX 50 program. Had the AMX CdC survived until this period, it would likely have evolved to carry either of these two weapons.

Layout of the fighting compartment in the manually-loaded configuration.
Source: Mémoire des Hommes

The CdC had a rather unique ready rack layout, even in its manually-loaded configuration. Thirty-six rounds were stored below the turret ring, facing nearly upside down in a crown or carousel covered by a metal sheet. The crown could rotate independently of the turret to present a new round to the loader, who had a small door next to him. This layout greatly simplified his job, as he only had one specific place to access the ready rack, and it freed space in the crew compartment. The metal cover for the rack may have also increased the survivability of the crew somewhat in case of ammunition detonation, but this would have depended on whether its thickness could stop fragments or not. Conversely, it may actually have been intended to provide additional protection for the ammunition in case of penetration by low-energy fragments and small-caliber ammunition.

Layout of the turret and ammunition crown controls as of January 9th, 1946.
Source: Mémoire des Hommes

Fifty-four additional rounds were available, 24 in the bustle, and 30 in the front hull, at the right. It is unclear exactly how that latter rack could be accessed from the inside, so it may have been purely intended to replenish the bustle rack from the outside, while the easily-accessible bustle ammunition was used to replenish the carousel. The presence of an unprotected bustle rack alongside a covered carousel is quite surprising from a survivability standpoint. Compared to Cold War vehicles, 90 rounds of ammunition was excellent for the caliber, but more or less in line with the Tiger II and the AMX M4. If one also considers the bustle rack as ready ammunition, then the CdC carried a whopping 60 ready rounds, nearly as many as Western Cold War tanks with 90 or 105 mm guns (or the Chieftain) carried in total.

The secondary armament consisted of one 7.5 mm MAC 31 Reibel magazine-fed machine gun mounted to the left of the driver and operated by him (but seemingly fixed) and the same machine gun mounted coaxially to the gun. Twelve drum magazines were installed to the right of the driver for his machine gun, and 6 on the turret roof inside the turret for the coaxial machine gun. Assuming the magazines carried 150 rounds each, as usual, this would be 2,700 bullets in total.

Automatic Ejection and Loading Device

Layout of the proposed autoloader and ejection system in the turret.
Source: Mémoire des Hommes

Automatic loading and ejection of spent cases were also contemplated. This made a lot of sense considering the difficulty of manually handling the very long 90 mm rounds. In this configuration, the carousel held 35 rounds instead of 36. The autoloading and ejection mechanisms were very complex but relied on springs and compressed air/water pistons for operation.

The loading process can be separated into 3 phases. The gunner would use his command stick (which also acted as a firing trigger) to select either an AP or HE round (respectively marked as “R” for Rupture or “E” for Explosif). The clamps retaining the round would open, while the clamps of the autoloading mechanism would grapple the round and rotate it. At this point, the round would be parallel to the gun and offset to the left of it. The mechanism would then rotate around the forward axis to place the ammunition in the gun breech’s axis (2nd phase). In the last phase, the round would be automatically rammed inside the breech.

Plan of the components and layout of the autoloading mechanism.
Source: Mémoire des Hommes

After firing, the empty case would be received by the ejection mechanism. The mechanism could hold 2 cases, one waiting, and one in the process of being ejected. The empty case would have been ejected out of an obturator at the base of the turret rear. The ejection also triggered the evacuation of gases outside of the crew compartment. The entire mechanism itself worked for any position of the turret and gun.

Plan of the ejection mechanism.
Source: Mémoire des Hommes

Protection and Survivability

With the exception of the cast gun shield, the vehicle used only welded steel plates. The front plates and gun shield were both 30 mm thick and well-sloped, while the other surfaces were all (except for possibly the floor) 20 mm thick and nearly vertical or horizontal. All-round protection would thus be expected against small arms and shell fragments only, although a level of resistance against US and Soviet armor-piercing 12.7 mm bullets was possible. The front might have been able to handle 14.5 mm bullets and 20 mm AP rounds, especially the area behind the gun shield, due to the locally spaced configuration of the armor and the extreme slope of the gun shield itself.

Although the turret ring sat above the hull roof, the turret was shaped specifically to hide it, limiting the likelihood of bullets and fragments jamming it to some degree.

An automatic fire extinguisher was located to the left of the crew compartment, behind the driver. Overall, the CdC followed a very similar philosophy to the American M18 Hellcat and the British Avenger of WW2, both being lightly armored but highly mobile turreted tank destroyers.

Powertrain

Following WW2, France was stuck with no indigenous solution for a high-power engine. Fortunately, the French managed to get their hands on Maybach factories, engines, and blueprints in their occupation zone in Germany. German components were extensively used and studied in early post-war powertrains.

In the case of the CdC 90, as well as other members of the AMX M4 family, the Lorraine 40t and the Somua SM, the choice fell on the Maybach HL 295 fuel-injected gasoline engine and the synchromesh AK 5-250 5-speed gearbox, a derivative of the AK 7-200 used in the Panther. This engine was developed by the Maybach design team in Vernon and was supposed to be built by the Maybach factory at Friedrichshafen, with Renault being considered as the most suitable option for French production.

The HL 295 was a water-cooled, fuel-injected gasoline V12. It was essentially a higher displacement version of the HL 234 (fuel injected, reinforced HL 230), going from 23 L to 29.5 L. Plans indicate that 27.5 L was initially considered. The HL 295 was 1,392 mm long, 1,060 mm wide, and 1,200 mm tall. In comparison, the 230 was slightly smaller, being 1,310 mm long, 951 mm wide, and 1,185 mm high. The French appreciated the compact nature of the Maybach engine, in particular its short length, which would minimize engine compartment size and weight.

This increased displacement was sought both as a way to ensure it would reach the desired performance, and to increase its future potential. The French initially thought that it could reach up to 1,200 CV (Metric horsepower or 0.986 hp), but it became clear by 1950 or so that 1,000 CV at 2,800 rpm was the most they could hope for. This is in line with fuel-injected engines of similar displacement, like the American AVSI-1790-8.

In practice, various reliability issues meant that the HL 295 was usually operated at 850 CV at 2,600 rpm. Maximum torque of 2,403 Nm was obtained at 960 CV at 2,800 rpm in one test, and usually varied between 2,354 and 2,550 Nm over the operating range of the engine. Fuel consumption varied between 230 and 250 g/CV.h.

Characteristics of the third prototype of the HL 295, as installed later on the SOMUA SM.
Source: SHD Châtellerault AA 503 1H1 27

At 34 tonnes and 1,200 hp, the CdC 90 would have had a whopping 35.3 hp/t power-to-weight ratio, far beyond even the requirements of the FINABEL 3A5 (or Europanzer) program of 1957. Even with the more conservative value of 850 hp, the CdC would have kept 25 hp/t, well in excess of most tanks of the period.

The transmission was located at the very rear of the vehicle under two large ventilation fans. In front of it was the engine. This installation occupied half of the length of the hull. Interestingly enough, this layout was low enough to allow full gun depression to the rear. However, it seemingly contributed to an increase in hull length, as the contemporary AMX M4 was nearly 50 cm shorter, with the fans on either side of the engine.

Engine compartment of the Chasseur de Char de 90 mm.
Source: Mémoire des Hommes

Suspension

The suspension was probably the most peculiar aspect of the Chasseur de Chars. The spring element chosen was the torsion bar, which was nearly the norm by this point. However, unlike contemporary French, US, and Soviet vehicles, these were mounted internally along the hull sides, going towards the front at an angle (parallel to the front-rear axis of the vehicle). The closest equivalent in a production vehicle would be the Christie-type suspension with coil springs also being mounted along the sides at an angle, although torsion bars would likely have more desirable properties. Why AMX went for such a radical design on this specific vehicle, when the M4 and 120 mm SPGs used regular transversely-mounted torsion bars, is unclear. A possible explanation is that the engineers wanted to reduce the height of the vehicle and could afford to sacrifice some of the width, which would make sense for a tank destroyer.

Outside of the sprocket and tensioning wheel, there were five double road wheels per side, each spaced 1.04 m apart. These were extremely large, with a diameter of 1 m. In this regard, they remained somewhat similar to the large wheels used on German and French interleaved suspensions. There were also three 300 mm diameter return rollers per side.

This suspension offered an impressive range of travel for the road wheels: 200 mm bump and 160 mm rebound, for a total vertical travel range of 360 mm, well above that of contemporary vehicles, limited to around 250 mm or less. Only British Cruisers or the Panther could match or exceed this level of performance. Overall, this suspension would have offered excellent mobility.

Layout of the suspension. The mounting points for the torsion bars can be seen on the right.
Source: Mémoire des Hommes

Mobility

Two 550 L and two 300 L fuel tanks were located in the engine compartment, providing an impressive 1,700 L capacity. Post-war gasoline-powered French vehicles typically carried a much greater fuel capacity than their Western counterparts to ensure an adequate (300 km) range. The CdC is referred to as having a 6-hour autonomy without refueling. Assuming that this was with a 300 km range, it would require a maximum speed of at least 50 km/h. However, if French requirements involved some off-road driving or an actual range greater than 300 km, it would be absolutely possible to go beyond this limit and towards 60 km/h or more.

In any case, the suspension and powertrain easily allowed such high speeds. Indeed, the CdC might actually have been able to achieve more than 80 km/h on roads, like the American M18 Hellcat.

Going by the ground contact length of 416 cm per track and 40 cm track width, the total ground contact area would be 16 640*2=33 280 cm². For a combat weight of 34,000 kg, this gave a ground pressure of 1.02 kg/cm² or a bit over 14.2 psi. Ground clearance was 400 mm, roughly standard for the time. The CdC’s relatively narrow tracks resulted in a somewhat high ground pressure for the period. Indeed, the ground pressure of a Comet Mk I Cruiser Tank was 13.85 psi. The Sherman with the HVSS suspension, with a more favorable ratio of track width to vehicle weight, had a ground pressure of 11 psi. This limitation was probably inevitable considering the choices with the layout of the suspension, the width taken by the carousel, and transport requirements.

Conclusion

The French showed relatively little interest in tank destroyers during the interwar period, restricting themselves to concepts of anti-tank guns slapped to existing hulls or powerful and heavily armored vehicles dedicated to the protection of intervals between fortifications.

The defeat at the hand of German tank formations in 1940 and the generally intense use of armor during WW2, led post-war France to make a considerable effort in the design of dedicated anti-tank vehicles, be they HEAT (High Explosive Anti-Tank) slingers such as the ELCs, or ATGM carriers or AT gun carriers such as the S35 and R35 hulls with 17 pounders. The AMX CdC, however, used the most original design philosophy out of all these concepts: a turreted vehicle with a gun shooting kinetic energy projectiles with similar power to the medium tank, with an emphasis on high mobility, lower weight, and smaller size.

Unlike other members of the AMX M4/50 family, which even participated in the Bastille Day parades, the CdC never spawned any prototype. The closest thing to a spiritual successor would be the Lorraine 40t, also lighter than the medium tanks, thinly armored, and equipped with a normal (by French standards) gun with an autoloader. At present, it is unknown when and why the AMX Chasseur de Char de 90 mm project was terminated.

AMX CDC. Illustrations by the Glorious Pavel Carpaticus funded by our Patreon Campaign.

AMX Chasseur de Char de 90 mm specifications

Dimensions (L x w x h) 9.23 (gun locked for travel)-7.38 (hull) x 3.25 x 2.78 m (top of cupola)
Weight 30 t empty, 34 t fully loaded
Crew 4 (Driver, Gunner, Loader, Commander)
3 (Driver, Gunner, Commander) with autoloader
Propulsion 2.5 litre 6-cyl Daimler petrol, 55 hp (41 kW), 18.3 hp/ton
Number of gearbox speeds 5
Engine Maybach HL 295 water-cooled V12, 1,200 hp expected
Fuel capacity 1700 L
Suspension Longitudinal torsion bars
Ground clearance 400 mm
Top Speed Unspecified, beyond 50 km/h
Autonomy 6 h of travel
Armament Schneider 90 mm SA45 rifled gun (90 rounds)
2 x MAC 31 7.5mm machine guns
(1 coaxial, 1 hull, 2,700 rounds)
Armor Welded and cast steel, 30 to 20 mm

Sources

Mémoire des Hommes (AMX CDC)
Mémoire des Hommes (90mm rounds)
Armement de gros calibre, Tauzin & Marest, 2008 (90mm SA45 data)
Les Archives de Châtellerault, Colasix (HL 295 data)
Panzerworld (88 rounds)

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