Saturday 4 June 2016

AMX 38: A Tank Between Classes

The results of the French competition for a new light tank in the mid 1930s were unclear. On one hand, the army made a deal with Renault to produce 300 light Renault ZM tanks. The tank entered service with the name Char léger Modele 1935 R,or Renault R35. A year later, the FCM 36 was accepted into service, which was more promising according to the infantry commanders. Doubt was cast on the production of the R35, but it was never cancelled, and it became the infantry's most numerous tank. Right before WWII began, the AMX 38 appeared, another tank that could have been accepted into service with the French army.

Match the FCM 36

The attention on the FCM 36 was no coincidence. Yes, the tank was the heaviest and most expensive out of all the participants, but it had two important advantages. One was the diesel engine, more economical and suitable for use in a tank. The other was even more important. The FCM tank was built entirely from rolled plates held together by welding. Other French medium and light tanks used cast hulls and turrets, assembled with rivets on frames.

Trials of the Renault R35 in June of 1937 illustrated the difference between cast and welded parts. According to the second edition of the technical requirements, the new light tanks must have armour that completely protects them from the 25 mm autocannon. In theory, 40 mm should have been enough to provide this. In practice, out of 22 25 mm shells fired from 0-1000 meters, 13 penetrated the armour. The case with 37 mm guns was even worse: 14 penetrations out of 18. It is not surprising that the FCM 36 was viewed with even more interest after that test. The idea of using its turret instead of the APX R on the Renault and Hotchkiss light tanks was also proposed.

Initial design of the AMX light tank, dated March 26th, 1938.

Meanwhile, Renault went through a production metamorphosis. In late 1936, the tank production branch of the automotive giant was nationalized. The new organization was named Ateliers de construction d'Issy-les-Moulineaux, or AMX for short. Production of the Renault R35 tanks and Renault UE tractors was retained, as was the heavy Char B tank. In 1937, the BE-AMX design bureu began a series of projects, starting with light armoured cars and engine with heavy tanks, later turning into superheavies.

Transmission diagram of the AMX 38.

One of these projects was a light tank, the work on which began in July of 1937. According to the initial concept, the 10 ton class tank would have a 100 hp CL4 diesel engine designed by Compagnie Lilloise de Moteurs (CLM), subordinate to the Peugeot conglomerate. The use of a diesel engine as the power plant was directly influenced by the FCM 36, and is only one sign of the inspiration. The tank on the draft provided on March 26th, 1938 has nothing in common with the Renault R35. Blueprint 0-130 is titled "light tank design with a rear engine". In June, an index appears on the blueprints, which is later made official: Char léger AMX 1938, or AMX 38.

The index  Char léger AMX 1938 was first used in blueprint 0-155 on June 13th, 1938. Note that instead of the APX R turret, the FCM turret is depicted.

The new tank was devoid of cast armour. Instead, it used 40 mm thick rolled plates, bent into complex shapes in places. The front plate was made from one piece of armour, as was the rear plate. As with the FCM 36, the pieces were joined by welding. The tank was longer than its predecessors: the full length of the hull as of June 1938 was 5034 mm, 80 cm longer than the R35 and 55 cm longer than the FCM 36. The result was an increase in mass from 10 tons to 13 tons. Nevertheless, the effective power was greater than that of the FCM 36, at 7.7 hp/ton compared to 7.4.

The longer hull wasn't just a whim of AMX engineers, it was done to increase the length of trenches the tank could cross. Despite the inspiration from the FCM 36, the tank's designers did not include fully sloped side armour. The sides were sloped around the turret, but the side of the engine compartment were flat.

Layout of the AMX 38's hull.

The suspension of the AMX 38 deserves a special mention. The suspension of the R35 with its horizontal springs and five road wheels per side was deemed unsuitable for an infantry tank. The first attempts to modernize the R35's suspension started in 1937, when the number of wheels was increased. In some ways, the designers made a step backwards, as the new suspension for the D1 and D2 tanks reminds one of the Renault NC.

The springs in the AMX 38 were also vertical, but unusual. There were two springs held together by a balancer arm, attached to the hull in the center. Each spring was attached to a bogey with two 218 mm wheels. The clever system was very successful: due to a large amount of road wheels, a large contact surface was achieved. The tank drove very smoothly, which was important when driving off-road. The version of this suspension for the Renault R35 had 12 road wheels per side, more than the FCM 36 (9 per side). The longer AMX 36 had even more wheels; 15! The AMX suspension offered a very smooth ride, which improved accuracy on the move.

A new turret was designed in November of 1938. On blueprint 0-190, it still has the short barreled SA 18 gun.

According the the initial designs, the tank would have an APX R turret, as it was present on blueprint 0-130. However, the military was quickly disappointed with it, and it did not last on the AMX 38 for long. In June of 1938, it was replaced by the Tourelle FCM. The project remained in this form until the end of 1938.

Not Enough Power

In late 1938, French infantry command decided that the effective power of the tanks currently in service is insufficient. A new requirement was announced: the effective power of new tanks had to be more than 10 hp/ton. The CL4 engine became unsuitable for the AMX 38. It didn't take long to find a replacement in the form of the 4 cylinder 130 hp diesel produced by Ateliers de Construction Mecanique l'Aster, who had extensive experience developing engines, including diesels. Aster also worked on many other tank engines, including 500 hp ones for heavy tanks.

AMX 38 prototype, Satori, 1939.

Next, the AMX 38 lost its turret. Trials showed that when firing from the 37 mm SA 38, the welding seams on the FCM turret began to crack. That put an end to the idea of using that turret on all tanks. In a short time, BE-AMX engineers designed their own turret inspired by the Tourelle FCM. It was also welded, but much simpler than its predecessor. Initially, the new turret was designed for the SA 18 gun, but was only built for the longer SA 38.

The amount of observation devices in the turret decreased to three, but this was compensated with one technical novelty. Instead of a commander's cupola, an observation periscope designed by Polish designer Rudolph Gundlach. First used on the TK-S tankette, the Gundlach periscope had a very well though out design and allowed the user to swap out damaged optics in battle. This revolutionary design is better known as the MkIV, and was later used on vehicles of many nations.

As with the FCM 36 turret, the AMX design was very narrow due to its sloped sides. Compared to them, the front plate which is positioned at almost a right angle looks very odd.

The same tank from the right. The prototype used a long barreled SA 38 gun.

The first prototype, registration number W 0231, was built in the spring of 1939 and was tested at the Satori proving grounds, south of Versailles. Visually, the tank was very different from the light tanks built in France before. The long and narrow tank weighing in at 13.5 tons was reaching the boundary between light and medium tanks. The armament was decisively light: a 37 mm SA 39 gun and a MAC Mle. 1931 coaxial machinegun.

While other French light tanks gave the driver at least a two piece hatch, the AMX 38 driver's hatch consisted of only one. This was less comfortable, but better at resisting shells. The hatch had an insert which could open up during travel. Even though the tank was very long, it was still equipped with a tail to aid it in crossing wide trenches.

The AMX 38 was the longest of the French interbellum tanks.

The AMX 38 showed itself well in trials, reaching a maximum speed of 25 kph. This is not much, but it was enough for an infantry support tank. At the same time, the military's appetites grew. In August of 1939, General Louis-Marie-Joseph-Ferdinand Keller was appointed as the Inpector of the Armoured Forces. By the end of the year, he made some depressing conclusions regarding the armament and armour of his vehicles. Of course, the SA 38 was better than the hopelessly obsolete SA 18, but calculations showed that it could only penetrate 30 mm of armour from 100 meters. This gun was only a half-measure. The skeptical Keller had 40 mm as his goal. A plate of that thickness could be penetrated by German 37 mm guns (although, to be fair, only at point blank range).

Like most French light tanks, the AMX 38 had a tail.

Keller's conclusions led to new requirements. Now, the thickness of armour for light tanks was 60 mm, and the mass ranged from 15 to 20 tons. The effective power had to remain the same: 9-10 hp/ton. The 37 mm SA 38 gun was rejected in favour of the 47 mm SA 35, which was used on the Renault D2, B1 Bis, and Somua S35 tanks. Together, these requirements spelled the end of the AMX 38 in its current form.

A Victim of Bureaucracy

Engineers from Issy-les-Moulineaux reacted quickly to Keller's new requirements. On December 11th, 1939, a reworked AMX 38 project was presented, labelled Char léger série. Its full length grew to 5279 mm, only 10 cm shorter than the medium Somua S35. The mass grew to 16.5 tons. The designers did not thicken the armour to 60 mm around the entire perimeter, reasoning that it will only lead to excessive increase in mass. Only the front armour was thickened, which is reasonable, as that is where most hits land. Due to the longer hull, an extra road wheel was added to the rear on each side. In general, the design was similar to the previous variant.

The mass produced AMX 38 would have looked like this.

The 47 mm SA 35 gun was much longer than the 37 mm tank guns, and the turret had to be designed anew. Only the turret ring remained the same at 1120 mm. The new turret was closer to the Tourelle FCM. Gundlach's periscope was removed and replaced with another observation device pointing to the front. Rolled plates were also removed, and the turret was once again cast. The total height of the tank with the turret remained the same: 2270 mm. 

A 160 hp 4 cylinder Aster engine was supposed to be used in the heavier AMX 38. Thanks to this, the effective power of the production AMX 38, often called AMX 39, remained within the bounds given by General Keller. The performance of the tank was also retained at the same level.

Diagram of the new AMX 38's hull.

While most work on the new AMX 38 was done in December of 1939, there are blueprints dated as late as March 14th, 1940. The resulting vehicle was more similar to an infantry tank rather than a light tank, whose characteristics were close to the Infantry Tank Mk.III, also known as the Valentine. If the French infantry had such a tank, then things would have gotten tough for the Germans. However, history does not know the word "if". Even before the German invasion on May 10th, 1940, the fate of the AMX 38 was far from decided.

On March 14th, 1940, documentation on the "production" AMX 38 was reviewed by a commission headed by Keller. At the same time, another project was being reviewed, not just from anyone, but from Renault! Nationalization of its tank branch didn't stop the company from fighting for military contracts. The three-man 16 ton tank received the index DAC1. Looking at both projects, the commission decided to widen the scope of the sudden competition and send requirements to FCM, Hotchkiss, Panhard, and Somua.

Despite the 47 mm gun, the inside of the turret was rather roomy. For a French tank, of course.

The fact that a world war broke out more than half a year ago was of no consequence for the commission. The next review was on May 14th. Right around that time, tens of FCM 36es were being destroyed south of Sedan. Renault presented the DAC1 once more, but as a wooden model this time. AMX presented a project that no factory documentation survived on. The tank would have had 60 mm thick armour all around and a 250 hp 6 cylinder Aster engine. AMX proposed the tank as a potential design for 1941. The decision of the commission was curious: it decided to wait for other participants, but the designs from FCM, Hotckiss, Pahnhard, and Somua never arrived. It's easy to understand them, as they had more important things to do at the time. Factories hurriedly produced existing tanks and armoured cars.

One month after the meeting, Paris fell. The AMX 38 could have been a mighty threat in its current form, but the fate of the light tank was a sad one. General Kelle's fate was also unfortunate: in August of 1944, the retired general was arrested by the Germans and on November 16th, 1944, he died in the Buchenwald concentration camp.

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