It was the menace of the German submarines that so nearly brought defeat to the British in World War II. The U-Boats wreaked havoc on Allied merchant ships and their vital cargoes, but in turn suffered horrendous losses, vanquished by the superior tactics and dogged seamanship of their pursuers. Seventy per cent of U-Boat crewmen perished at sea. This is the story of the U-Boat wars, from 1914 to 1945, recreated from the experiences of German survivors, a tale of constant danger.