France had a vast fleet of tanks, predominantly well-armored but slow tanks of a variety of roles- including the Renault R-35, Hotchkiss H-35/38, FCM-36, and a few others. Their bread and butter tanks, the Somua S-35, and their heavy tank role filled by the Char B1 BIS. All these tanks are famous, more or less, despite France's collapse in the war. But, even as vast and complicated as it was, the Char B1 was not the biggest tank planned for the war...
In 1940, shortly before their total defeat, the French government pushed it's arms manufacturers, ARL, AMX, and FCM to cook something up that would halt the German Blitzkreig. All three companies believed salvation lay in a tank that was, for the weapons brought against it in the Panzer I, II, and III tanks available, invincible. ARL took the lead, and production began on a prototype of an experimental super heavy tank, the ARL Tracteur C. The exact genesis of the name is shrouded in mystery, though it's believed the designation "Tracteur" was intended to throw off German spies to the true nature of the project (believing it to be an artillery tractor and little else), and the "C" version indicates it was the third draft design of the vehicle.
The vehicle would feature two turrets, one mounting a more traditional 47mm gun, while the larger turret would house a massive 90mm cannon. For a time when 50 caliber machine guns were considered "anti-tank" weapons, a 90mm gun was unheard of. The prototype was being assembled when France collapsed. After the ARL factories were captured by the German Wehrmacht, the vehicle was studied briefly, as it was in an incomplete state, and the engineers building it had worked hard to destroy what information they had on it from blueprints on down. Today, only 2 photos are known to survive:


What happened to the vehicle after the German conquest of France is unknown. As it was incomplete and the plans were scattered at best, it is believed the Germans scrapped the vehicle. Today, historians debate what the vehicle ultimately would have looked like when finished, though most agree that the Tracteur C would have had little, if any effect on the Blitzkreig.
Consider this a wistful momento of what might have been...
