The French Char B1 was one of the most distinctive heavy tanks of the interwar period and the Battle of France. Conceived in the early 1920s as a self-propelled gun for breaking through enemy fortifications, it mounted a 75 mm howitzer fixed in the hull. In the 1930s, as the threat of enemy armour grew, a 47 mm gun in a small turret was added, turning it into a dual-purpose battle tank. This compromise gave the B1 its unusual appearance, with large tracks running around the hull and armour protection that echoed First World War designs. Development delays and high production costs meant that by the time the main version, the Char B1 bis, entered service in the late 1930s, it was already outdated in mobility but formidable in armour and firepower. The tank’s strengths lay in its protection and guns. With up to 60 mm of armour, the B1 was nearly invulnerable to German 37 mm anti-tank weapons in 1940. Its 75 mm hull gun could smash fortifications and enemy vehicles, while the 47 mm turret gun was effective against tanks. However, the turret was manned by a single commander, who had to load, aim, fire, and direct the vehicle—an overwhelming task compared to the multi-man turrets of German and British tanks. Strategic mobility was also a weakness: heavy fuel consumption and limited range restricted its usefulness for mobile warfare, while French doctrine envisioned it as a breakthrough weapon for methodical offensives rather than rapid exploitation. In combat during the German invasion of 1940, the B1 bis showed its power in direct engagements. At Stonne on 16 May, Captain Pierre Billotte’s tank Eure destroyed thirteen Panzer IIIs and IVs in minutes, surviving 140 hits. German accounts also record frustration, as even captured 47 mm anti-tank guns could not penetrate its armour. Despite these successes, most losses came from artillery and anti-tank guns, which could outmaneuver or overwhelm the slow-moving French tanks. Germany’s faster, better-coordinated Panzer divisions exploited these limitations, bypassing and isolating French heavy units. Production remained limited due to cost and complexity. Built by several manufacturers, including Renault and AMX, each Char B1 cost 1.5 million francs, consuming half of France’s infantry tank budget. By 1940, only a few hundred were available, too few to counterbalance German numbers and mobility. After France’s defeat, captured B1s were reused by the Wehrmacht as flamethrower tanks, artillery carriers, or supply vehicles. The Char B1 thus represented both the strengths and flaws of French tank design before 1940: extremely powerful on paper and in duels, but too expensive, slow, and poorly suited to the fast-moving style of warfare that defined the Second World War.