In 1928, French general Etienne started a development program for a special type of vehicle, called Fortress Tank (Char de Forteresse), that was supposed to weight from 45 to 55 tons. The main idea was to create a heavily armored and armed vehicle, that would help fortify the Maginot line.

Company FCM was tasked with the project. In 1932, after several schematic proposals that looked just like raw outlines, the FCM engineers developed a proposal for a vehicle called Char BB. This 50 ton tank had 60mm of armor and was armed with a pair of 75mm guns with two machine-gun mini-turrets on the top. It was supposed to be propelled by a 600hp engine. Since the guns were protruding so much from the front, the developers had to add a "bumper" roller to the front as well to compensate for the weight distribution - this roller could also in emergency serve as a mine-clearing device.

A scale model was made and it was shown to general Etienne in September 1932. It was actually approved and FCM started working on a full-scale mock-up. At the same time however, a disarming conference took place in Geneva, imposing arms limits on its participants. This mostly affected the navy, but somehow, Char BB was included as well. The idea to build "fortress tanks" was shelved for 5 years and returned only in 1937.