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.

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.