"Wolfpacks," teams of German U-boats that attack at night, are sinking convoys of allied ships along with Britain's hopes of ever controlling the Atlantic. However, the development of radar allows escort warships to lock in on U-boats ten miles away. This new technology, plus the lucky discovery of German codebooks and equipment, gives Britain the upper hand, but the triumph is short-lived. Hitler orders the mass production of U-boats and the carnage continues. Britain needs America's help, and thanks to the Japanese, their wish comes true.