The first six months of 1942 saw the war assume a truly global dimension with the entry of the United States into the conflict. For the U-boat arm, the heavy coastal traffic off the eastern seaboard of the U.S. provided such fertile hunting ground that the high number of vessels sunk led this period to be christened by the submarine crews as the "second happy time." the belated introduction of convoy tactics by the US Navy saw U-boat victories off the U.S. coast sink to a low of just three in July 1942. Fuehrer der U-boote Doenitz now set out to exploit the gap in the mid-Atlantic where convoys were beyond the range and protection of allied aircraft. By 1943 the Wolf Packs were inflicting heavy losses on the convoys - the high point of the U-boat campaign in World War II. New footage helps US understand the on-going battle between hunter and hunted above and beneath the cold, grey waters of the North Atlantic - the most decisive theatre of World War II.