The Second World War and its many years of occupation led to stagnation of the French tank building school. The ARL-44, planned for production in 1944, was already obsolete compared to tanks of the USSR, USA, or Germany. French engineers had to quickly develop a tank that could deal with modern war no worse than a Tiger or IS.
Compared to their colleagues from other countries, the French had less experience in building tanks. However, instead of picking apart a captured tank and copying it, they decided to experiment. The result was very interesting.
While they did not copy anything outright, the French borrowed some technology from their "inherited" German E-series documentation. The first prototype, named AMX M4, was reminiscent of the King Tiger. It had the same suspension, with interleaved road wheels and internal shock absorbers. However, it had a rear engine and transmission. The tank was never built in metal.
A decision was made that the new tank had to have a more protected turret and a more powerful 100 mm gun. The French put the gun in an oscillating turret. The turret was composed of two parts. The gun was fixed in the upper part, and has no mantlet. Vertical aiming was achieved by moving the entire top part of the turret up and down. Horizontal aiming was done by rotating the lower part of the turret. This allowed the turret to be very small, due to a lack of gun elevation mechanisms. Additionally, one crew member could be eliminated by installing an automatic loader.
The first autoloader used a revolver drum-like cassette. The cassette fit 6 rounds, which had to be refilled manually.
The new tank was indexed AMX 50 100. Aside from the new gun, it received a better suspension, 120 mm of front armour, and a 1000 hp gasoline engine. In theory, the tank was supposed to accelerate to 60 kph, but tests never managed to get it over 51 kph. Even that result was pretty good for a heavy tank.
In 1951, during continued tests of the AMX 50 100, a new 120 mm gun was developed. The model with this gun was called AMX 50 120. The tank was developed as a counter to Soviet IS-3 and T-10 tanks.
Like its predecessor, it had an oscillating turret and an autoloader. The hull was changed. The front was "piked", like the IS-3. Aside from a 120 mm gun, the turret had 7.5 mm machine guns, to combat enemy infantry. The hull was cast, which increased its durability. The increase in mass decreased maneuverability. The French wanted the tank to accelerate to 65 kph. This would have required a 1200 hp motor, but the French never managed one that could achieve more than 850 hp.
The increase in caliber had a downside. While 100 mm shells were still serviceable, manually reloading a cassette of 120 mm shells was hellish labour.
The French were proud of their new tank. They considered it as mobile as a Panther, as powerful as an IS-3, as reliable as a Sherman. Even Germany was interested in this new tank, and made a preliminary contract to buy some AMX 50 tanks.
However, if you look past the developers' optimistic views, the AMX 50's real life applications were questionable. Its mobility and autoloader would give it an edge in quick battles, but its weak armour and large size made it completely unsuited for prolonged combat.
AMX 50 never made it to mass production. Only five of these very interesting vehicles were built. Many opinions exist as to why. Some historians claim that the tank was insufficiently protected, especially against HEAT. Due to the oscillating turret, it was difficult to protect the crew against chemical weapons, or radiation. Finally, oscillating turrets were not compatible with NATO's standardization plans.
There is another version. The tank was "buried" by corrupt officials. After the Korean war, America had a surplus of tanks, which had to be sold to someone quickly. Some French military officials made a profitable deal, and France got M47 Pattons instead of AMX 50s.