In the 20th century's greatest war, one battlefield held the key to victory or defeat—the North Atlantic. For five and a half years, German surface warships and submarines attempted to destroy Allied transatlantic convoys, most of which were escorted by Royal Canadian Navy ships, as well as the Royal Canadian Air Force. Telling a gripping tale, Ted Barris explains how Canadian forces kept Britain's hopes alive, then delivered a decisive blow to Germany's control over the high seas.