Saturday 5 March 2016

AMX 50: Five Years of Trial and Error

The second half of the 1940s was a dark time for a lot of tank building schools. Many projects were either downsized or cancelled completely. France was no exception. The only tank to make it out with relatively few problems was the AMX 13. Things were much more complicated for the ARL 44. This tank was such an obvious failure that it was removed from service shortly after starting production. Its successor, the AMX M4, suffered an even worse fate. The unending quest for an ideal tank described in this article resulted in the longest lasting project in French tank design history.

Longer, Thinner, Heavier

The AMX M4 project remained still for almost all of 1946. This is directly connected with the ARL 44 entering trials in March of that year. The first French post-war tank was late for almost a year, and trials showed that the vehicle needs extensive improvements. These trials couldn't have left the new tank unaffected. Sadly, the details of the trials are still unknown, but judging by the upcoming metamorphosis, the vehicle's stability was questioned.

Improved AMX M4 hull, blueprint dated January 17th, 1947

Work on the prospective heavy tank restarted by the end of 1946. The first results were demonstrated by AMX engineers in early 1947. The concept of a 50 ton medium tank did not change. The high power 90 mm gun and the turret that it was installed in remained unchanged.

The main difference was in the tank's chassis. The hull was lengthened from 6705 to 7413 mm due to an increased size of the driver's compartment. Thanks to this, the driver and radio operator received proper hatches in the hull roof. The longer hull also resulted in another road wheel being added. The upper front plate also received sloped cheeks, increasing the odds of a ricochet.

Various variants of the tank's armour were proposed. With a 120 mm thick front, the tank's mass would be 55.5 tons. Because of this, the thick armour was rejected.

This decision wasn't caused by excessive concern for the driver and radio operator. Diagrams indicate that this was the designers' method of improving the center of mass. On the initial design, the turret was shifted forward, which could negatively impact the load on the road wheels.

On the other hand, at what cost was this optimal weight achieved? The front armour was reduced to 80 mm, and even then the estimated mass of this medium tank was 54 tons. A variant with 120 mm of armour that would increase the mass by only 1.5 tons was also explored, but it did not go further than just theory. The 80 mm front armour was finally approved.

The AMX M4 looked like this in 1949. The project became more and more similar to the German Tiger II.

In 1947-48, the project was evaluated and re-evaluated in every conceivable way. By the beginning of 1949, designers were forced to admit that 54 tons was not the limit. According to revised estimates, the tank's mass was 54.6 tons, 13 of which were for the turret. The size of the new tank caught to to, and then exceeded, the Tiger II. Meanwhile, its armour was thinner than that of the Panther. Of course, the solution of the center of mass problem wasn't the end of this journey, but only one episode. 1949 will bring new radical changes.

Swings and Drums

In November of 1946, AMX proposed a 12 ton airborne tank. One of the features of this design was an oscillating turret, where the entire turret moved along with the gun when traversing vertically. This system was first used on the Panhard 201 armoured car, but the tank took it further.

The oscillating turret designed by FAMH (Forges et Aciéries de la Marine et d'Homécourt, better known as Saint-Chamond) was needed for a semi-automatic loading mechanism. The turret bustle housed two revolver type drums that each held 6 rounds. This system resulted in a rate of fire of 12 RPM. A long pause followed the 12 shots to reload the drums, but this was a worthwhile tradeoff, as 12 rounds was usually enough to deal with any target. The airborne tank didn't pan out, but the AMX 13 did.

FAMH oscillating turret design for the AMX M4.

The idea of developing an analogous turret for the AMX M4 was reasonable. The first designs on this topic are dated March 1949. At the same time, an alternative hull armour variant was being worked on. The slope of the front plate was reduced to 45 degrees, but the thickness was increased to 180 mm. The lower front plate was thickened to 120 mm. The hull became shorter (7237 mm), but the mass grew to 57,800 kg. As a result, the tank outgrew the King Tiger both by weight and armour thickness.

Proposal with a thickened upper front plate. The mass of this tank was 57.8 tons.

It's worth noting that the FAMH turret was more compact than Schneider's. Since it didn't have a large bustle with ammunition, the length decreased significantly. A separate 55 hp Maybach engine was responsible for rotating the turret. On the other hand, compactness meant nothing when it came to weight. The mass of both turrets was estimated to be identical, 13 tons. To compare, the King Tiger's turret weighed 13.5 tons.

In parallel with the oscillating turret, the issue of a tank destroyer on the AMX M4 chassis was explored in 1950. This designation was arbitrary, as the ARL 44 was reclassified as a tank destroyer at this time. The new tank destroyer was supposed to weigh 51.2 tons. Instead of a FAMH oscillating turret, it was supposed to have a large cast turret with a 100 mm gun. The hull was changed too. The front received a "chevron type" upper front plate, reminiscent of the IS-3's pike. As with the Soviet tank, only the driver remained in the hull of the AMX M4. The turret appears displaced, but this is not the case.

AMX M4 prototype, 1949.

The arbitrary nature of the tank destroyer designation is revealed by the various variants of the project. The predecessors of the 51.2 ton vehicle with 45 mm of armour were much heavier vehicles, and the projects dated spring of 1950 are unambiguously called "tank". They looked light from the outside, but the thicker armour increased their mass up to 70 tons. None of these designs made it off paper, but separate elements, like the pike nose, were implemented in metal.

The designers settled on the AMX M4 in 1949. Weighing all pros and cons, the hull remained in the 1947 configuration, keeping its 80 mm thick armour. The hull machinegun was removed. Formally, the assistant driver remained, but his role was mostly ballast. Doubts about the need for a fifth crew member grew. The turret was 120 mm thick in the front and 60 mm thick on the sides. In order to make the gun easy to service, the front of the turret could be removed.

Tank destroyer on the AMX M4 chassis. This vehicle was meant to have a 100 mm gun.

The tank was finally built in late 1949. The mass of the tank was 52 tons. The tank got a little heavier compared to the initial project, but a 1000 hp Maybach 295 engine maintained the estimated characteristics. In trials performed in 1950, the tank accelerated to 51 kph on roads and 35 kph off roads. This was a decent tank that could serve as a replacement for the ARL 44. The latter had problems, as mass production lagged behind schedule and reviews from the military were less than stellar.

The military was no longer satisfied with the AMX M4 prototype. This time, the armament was the reason.

New Gun

In spring of 1950, work on a new AMX M4 with a 100 mm gun began. These designs were sent to the archives, but not the gun. The muzzle velocity of 1060 m/s was desirable for the military, as it had superior penetration to the 90 mm gun. This gun would let the AMX M4 fight any tank of the era. It's not surprising that the military wanted this gun not only in a tank destroyer, but in a tank.

Blueprints of a 100 mm gun in an M4, June 1950.

By June 6th, 1950, the draft of an AMX M4 with a 100 mm gun was ready. The design fitted 60 100 mm shells into the tank, 14 of them in the turret (9 in the drum, 5 in the turret bustle). The new gun increased the mass of the turret to 15 tons and the mass of the tank to 53.7 tons. The military didn't mind, and the AMX M4 prototype received a 100 mm gun by the end of 1950. The removable front armour was done away with, and the front of the turret was now one whole armour piece. Trials showed that this was a good decision. The index of the tank was also changed: the M4 was dropped and the full name of the tank became "Char Moyen de 50 tonnes AMX". Later, this title transformed into a simpler "AMX 50". Often this tank is called "AMX 50 100", but this designation was never used.

AMX M4 with a 100 mm gun, January 1951.

The results of trials earned the approval to build two more prototypes of an improved AMX 50. The turret design changed somewhat, as did the upper front plate. The mass of the vehicle reached 55 tons after these changes. In April of 1951, the first AMX 50 was shown during a demonstration of new weapons and vehicles on the territory of the 32nd Artillery Regiment HQ, quartered in Bad Lobenstein, Germany. 

On July 14th, 1951, both tanks triumphantly drove down the streets of Paris in a parade. This parade was notable in that many experimental vehicles took part in it. Nevertheless, the new tanks and SPGs caused quite an impression. It's worth noting that the AMX 50 prototypes were slightly different. One was exactly identical to the reworked AMX M4. The other received a new turret. Its hull was also widened to 3400 mm due to wider mudguards.

AMX 50 prototypes, Paris, July 14th, 1951.

Sweden became very interested in these French 50 ton tanks, as work on the EMIL medium tank was currently underway. In January of 1951, a delegation visited France and familiarized itself with the AMX M4 and its new 100 mm gun. France and Sweden actively exchanged information; it can be said that the French tank directly influenced the Krv project. Of course, the Swedish tank had a different loading mechanism from the start.

Another country interested in French tanks was the United States. The Americans were so impressed by the AMX 50 that they negotiated the delivery of the first prototype for full trials. The first tank was loaded onto a ship and sent to the United States in late December of 1951. Trials began on January 10th, 1952. The first stage finished in March of 1952, and the final tests were finished a whole year later, March 13th, 1953.

The Americans had a good reason to be interested in the tank. Since January 1951, they were building their own T69 tank, whose design was similar to the French design. The loading mechanism was different, but the principle of a revolver type drum was the same.

AMX 50, second prototype.

The conclusions of the American specialists deemed the AMX 50 turret interesting, but pointed out a ton of vulnerabilities. It was much easier to jam this turret than a traditional one, and a 90 mm American shell penetrated even its front with relative ease. A proposal was made to increase the front armour to 90 mm, so the 90 mm shell would penetrate it from 1775 meters instead of 2414 meters.

By the time the tank's tracks hit American soil, its fate was sealed. The growing appetites of the French military in 1951 meant the end of the AMX 50. In their minds, a new vehicle took shape, one with a much more powerful gun...

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