Just before midnight on October 13th 1939, a lone U-Boat slipped through one of the Royal Navy's most important bases on an impossible mission - an attack on a British Battleship in the safety of the anchorage at Scapa Flow.
After the German U-boats sank more than three million tons of shipping, a new and vital source of intelligence gave the Allies an opportunity to transform the war and shape victory from defeat in the Atlantic.
In the Spring of 1943 the tide had turned; the Allies were winning the technological race. The U-boats fought on against the odds, but the hunter had become the hunted. The Allies struggled to achieve final victory in the Atlantic.
