In that global conflagration, only one battle—the struggle for the Atlantic—lasted from the very first hours of the conflict to its final day. Hitler knew that victory depended on controlling the sea-lanes where American food and fuel and weapons flowed to the Allies. At the start, U-boats patrolled a few miles off the eastern seaboard, savagely attacking scores of defenseless passenger ships and merchant vessels while hastily converted American cabin cruisers and fishing boats vainly tried to stop them. Before long, though, the United States was ramping up what would be the greatest production of naval vessels the world had ever known.