The B1bis was the french army's heavy tank during WW2. This one fought at the battle of Stonne in may 1940 during german invasion of France. This is a very good video and shows a lot of detail. The Char B1 was certainly a nasty suprise against what the Germans had at the time in a straight fight, its armour was clearly superior to the 20/30 mm armour the Germans had, however it stilll overall fared poorly against properly prepared Panzer units supported by artillery. The engine grill on the side could be penetrated by 20 mm AT guns.
At first the French tanks were used in an infantry support and defensive role. On the morning of 16 May a counter-attack was led by the French tanks. The 3rd company of the 41st Tank Battalion (B1bis tanks) went into attack without infantry support. They met Panzer Regiment 8. A single B1bis tank (Lieutenant Bilotte's "Eure") pushed into the town itself, into the German defences, and then withdrew after attacking a German column and destroying two PanzerKampfwagen IV tanks, 11 PanzerKampfwagen IIIs and two PaK 36 anti-tank guns single-handedly. Billotte's Char B1bis tank received 140 hits from enemy tanks and guns, but none were able to penetrate the tank's heavy armour.