Its not really a weapon but it was called the Magno-Line or something. Anywho it was supposed to be the ultimate defensive wall. It had bunkers
walls and cannons all facing Germany. It spaned the whole German-French border. How did the Germans possibly defeat it in WWII. They went through
Belguim and took Paris. When they fianally needed to eliminate the soldiers occupying it they simply hit it from the rear.