The American explorer made the claim he had unearthed a World War 2-era German submarine more than 40 years ago. Known as U-boats, the German vessels terrorised the Atlantic Ocean throughout the war, sinking numerous cargo ships as they travelled between Europe and America. However, the tide turned against the Nazis, and by the end of the war the Allied Forces had sunk more than 600 German subs. While the U-boats were a deadly weapon at the disposal of Nazi leader Adolf Hitler, they were also said to have been used in smuggling operations. Throughout the war, a secret fleet...