The film tells the story of how during World War II, in order to sustain the combat effectiveness of the European Allies, the US needed to maintain the smooth flow of important sea lanes for transporting goods and personnel to Europe, and the Atlantic Ocean was a necessary route. The strategy adopted by the Allies was to send a fleet of merchant ships escorted by warships and planes to cross the Atlantic Ocean. Moving about 40 ships as a tightly integrated unit was not easy, and it was even more difficult to avoid being discovered by the cunning Germans.