When World War II began, the Char B1 was the only true heavy tank to be fielded by a Western European army, and the only one in the world aside from the Soviet T-35. It was conceived as early as the 1920s and this was reflected in its initial design, which featured large tracks going around the hull, which was of riveted construction. Protection reached a maximum of 60mm which made it practically invulnerable to all German ammunition except for the deadly 8.8cm flak/anti-tank gun. The turret was identical to that used in the S-35 medium tank and featured a 47-mm SA gun. However, the main armament was a hull-mounted 75-mm SA 35 gun, with a noticeably short barrel. The suspension consisted of 16 short roadwheels on each side, of which 12 were controlled by three bogies and the remainders had independent springs. Because the Char B1 was envisioned as a breakthrough tank, mobility was not a priority and this would affect its performance against the Germans after the 1940 invasion. Furthermore, the turret was operated by just one crew member which increased the workload significantly. As a result, the Char B1 struggled when used as a mobile reserve and despite taking out some Panzers, it was largely irrelevant to the outcome of the campaign. Surviving units were pressed into German service, and a planned successor, the ARL-40, was eventually completed post-war as the ARL-44 heavy tank.

A 1921 requirement by the Section Technique des Chars de Combat led by Gen. Estienne led to five different companies involved in developing mockups and later prototypes of what would be the Char B1 which initially carried an SA 34 L/27.6 gun. Only a small number were built before production switched to the improved Char B1bis with heavier armor, a longer-barreled SA 35 L/32 gun, and an uprated engine. A final variant was known as the Char B1ter with even thicker armor, a fifth crew member (mechanic), and limited five degree traverse on the hull gun. Captured units were used extensively by the Germans and modified for various roles including the PzKpfw B1(f) Farhschulewagen training vehicle, PzKpfw B1bis (Flamm) flamethrower, as well as a 10.5cm howitzer.