On May 20, 1940, the German army in northern France reaches the English Channel. In reaching Abbeville, German armored columns, led by General Heinz Guderian (a tank expert), severed all communication between the British Expeditionary Force (BEF) in the north and the main French army in the south. He also cut off the Force from its supplies in the west. The Germans now faced the sea, England in sight. Winston Churchill was prepared for such a pass, having already made plans for the withdrawal of the BEF (the BEF was a home-based army force that went to northern France at the start of both World Wars in order to support the French armies) and having called on the British Admiralty to prepare “a large number of vessels” to cross over to France if necessary. With German tanks at the Channel, Churchill prepared for a possible invasion of England itself, approving a plan to put into place gun posts and barbed wire roadblocks to protect government offices in Whitehall as well as the prime minister’s dwelling, 10 Downing Street.