AMX-50 Surbaissé - A Mighty French Autoloader - Tank Historia

AMX-50 Surbaissé – A Mighty French Autoloader

Few tanks are as unique, large and imposing as the AMX-50 Surbaissé, a mighty French machine that started out as a medium tank, grew into a heavy tank and settled as a main battle tank.

Developed shortly after WWII the AMX-50 line of vehicles incorporated many elements copied from German designs, even going as far as using Maybach engines.

Its fluctuating weight and ever changing role hampered the project and eventually became its downfall.

Contents

Background

The AMX-50’s story begins in WWII. Before falling under German occupation France had one of the most formidable tank forces in the world.

France’s progress was curbed when Germany invaded, but this didn’t stop them developing tanks in secret. A number of firms assisted in this, namely Laffley and Lorraine.

Extremely limited in funding, manpower and resources the French designers borrowed and incorporated many German design features, such as engines, tracks and interleaved road wheels. These secret activities resulted in the ARL-44, an obsolete and poor performing vehicle.

During the ARL-44’s development it became clear that it was not going to be good enough, so in 1945 the French workshop Atelier de Construction d’Issy-les-Moulineaux (better known as AMX) drew up plans for a new medium tank called the M4.

The ARL-44 was born out of limited resources and German influences. Unsurprisingly it was instantly obsolete. Image by The shadock CC BY-SA 3.0.

The M4 was armed with a 90 mm Schneider gun and closely resembled the Tiger II. Designers were limited to a maximum weight of 30 tonnes, which forced them to use laughably thin armor (30 mm at most).

The French military requested more armor, beginning what would become the AMX-50 series of prototype vehicles. These vehicles utilised oscillating turrets, autoloaders and many German principles.

If all went to plan, France would sell the AMX-50 to armies all over Europe rebuilding from the devastation of WWII.

AMX-50 100

The weight limit was increased from the M4’s 30 tonnes to 50 tonnes and the maximum armor was increased to 80 mm. Designated the AMX-50 in reference to the tank’s weight, the first prototype was delivered in 1949 and weighed 53.7 tonnes

The second AMX-50 prototype arrived soon after. Both tanks were fitted with 100 mm guns.

To keep the weight down designers opted to use an oscillating turret – a rather modern and unique choice at the time.

Oscillating turrets come in two halves; an upper piece and lower piece. The lower piece sits on top of the hull and controls rotation, while the upper piece contains the gun and controls elevation.

The AMX-50 100.
The AMX-50 100’s autoloader was situated in the rear of the turret.

Since the gun moves with the turret it can be mounted higher up, as it doesn’t need spare room for the breech’s movements. This also allows for a smaller turret ring and therefore a smaller and lighter hull.

Additionally, as the gun is locked to the turret they can easily accommodate an autoloader. This is because the gun is permanently locked in line with the loading mechanism, unlike autoloaders in conventional turrets.

Meanwhile, engineers were struggling to developing an engine that produced the required 1,200 hp. 1,200 hp ensured the 50-plus tonne tank had a power-to-weight ratio over 20 hp per tonne.

HL 295 engine.
The Maybach HL 295, one of the few engines that produced anywhere near the power needed for the AMX 50. Image by Thomas Vogt CC BY-SA 2.0.

This power-to-weight ratio was not random, it was a requirement by French military as the AMX-50 was supposed to be a mobile vehicle.

The German Maybach HL 295 and a Saurer diesel engine – both capable of about 1,000 hp – were the only engines available to French designers at the time that could produce anywhere near this power.

The hunt for a suitable powerplant would plague the entire AMX-50 project and eventually contribute to its cancellation.

AMX-50 120

In 1951, the French initiated a third vehicle, the AMX-50 120. As indicated by its name, this tank carried a 120 mm gun that was a relative of the powerful American M58 gun used in the M103.

The incorporation of this gun was a response to the IS-3, a tank feared by the west as it could knock out virtually all of their tanks while being immune to their guns. This fear led to the US developing the M103 and the British developing the Conqueror.

The AMX-50 120.
The AMX-50 120 brought significantly more firepower over the AMX-50 100, at the cost of weight and reliability.

But with a larger gun came larger ammunition, and as a result, a larger turret. A prototype was complete by 1953 but it weighed over 59 tonnes – a far cry from the 30 tonne medium tank envisaged in the 1940s.

The AMX-50 120 was re-classified as a heavy tank.

Concerned that the tank was too lightly armored the French produced yet another AMX-50 vehicle: the AMX-50 Surblindé.

AMX-50 Surblindé

The AMX-50 Surblindé, meaning “up-armoured”, was an attempt in in the mid 1950s to increase the AMX-50’s armor protection. It had a highly angled “pike nose” (similar to the IS-3) at the front of the hull.

While this increased the tank’s protection it also increased its height, forcing engineers to create a lower oscillating turret. The surblindé version was also heavier, reaching nearly 65 tonnes.

This extra weight increased the strain on the AMX-50 Surblindé’s drivetrain and its reliability dropped significantly.

The AMX-50 120 surblindé.
The AMX-50 120 surblindé was the heaviest of the five prototypes.

To make matters worse, advancements in HEAT ammunition meant thick armor was no longer as useful as it had been in the years prior.

Mobility was now key, so France created one final AMX-50 that they hoped would be the fast, mobile and powerful main battle tank of the future, for France and Europe.

However, this relied on engineers finally solving the problems with the Maybach powerplant.

Spoiler: this never happened.

AMX-50 Surbaissé

The idea of a main battle tank version of the AMX-50 resulted in the AMX-50 Surblindé. This vehicle was made lighter by reducing its armor and lowering the hull significantly, hence the name surbaissé, meaning “lowered”.

Development of this vehicle took place between 1956 and 1958.

The lower hull allowed for a taller turret, giving the gun more elevation. These changes reduced the tank’s weight to 57 tonnes.

Inside was a crew of four: a driver, gunner, commander and loader. The loader’s job was to replenish the autoloader.

AMX-50 next to an ARL 44.
The AMX-50 surbaissé was a monstrous vehicle. Its oscillating turret was gives it a distinct appearance.

This version, with its highly sloped frontal hull, enormous turret and long gun is the most well known version of the AMX-50 group of vehicles.

Its 120 mm gun was tremendously powerful, made even more deadly by its auto-loading system, although its reliability was reduced compared to the 100 mm autoloaders due to the greater size of its ammunition.

Next to the gun was a 20 mm coaxial machine gun. This was fitted to save using the main gun against lightly armored targets.

It was marketed as a vehicle that was as mobile as a medium tank with the firepower of a Conqueror. Unfortunately, the unsolved riddle of the Maybach engine raised its ugly head.

The AMX-50's 20 mm coaxial gun.
The AMX-50 surbaissé’s coaxial 20 mm meant it didn’t have to use precious shots out of its autoloader against weaker targets.

If the desired 1,200 hp was achieved, the AMX-50 was theorized to have a top speed of over 40 mph, but in practice only an 850 hp engine was fitted, giving it a top speed of 30 mph.

As it became clear the engine wasn’t going to make 1,200 hp, the AMX-50’s much touted mobility was nothing more than an empty promise.

There was no alternative either, as the lowered hull removed the possibility of installing other engines. Additionally, its oscillating turret was inherently difficult to seal against nuclear radiation or chemical weapons.

Cancellation

France had high hopes for the AMX-50 and very nearly began mass production, but reliability issues and continuous delays in creating a 1,200 hp engine meant the program was cancelled in the late 1950s for simpler, more conventional designs.

The effort wasn’t a waste though, as lessons learned with the AMX-50 project found their way into the AMX-30 and even the later Leclerc, which also used an autoloader.

The Swedish took some inspiration from the AMX-50 as well and incorporated it into their Kranvagn tank project.

The AMX-50 from the front.
The AMX-50 project came to a close for many reasons. It was too complex, too expensive and an engine couldn’t be sourced.

Its failure should not detract from the facts. A 60 tonne tank carrying an autoloading 120 mm gun and travelling at over 40 mph would have been an incredibly impressive feat – one that the French very nearly achieved.

The fact that France went from an occupied country without any real ability to produce their own tanks, to building a truly formidable machine, is a huge achievement in its own right.

Another Article From Us: The Kranvagn – Sweden’s Autoloading Heavy Tank

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The AMX-50 Surbaissé is the only remaining vehicle from the AMX-50 project that remains today. It can be seen at the Saumur museum in France.