Under Ten Flags

James Mason and Laurence Olivier were the two front runners for the role eventually played by Charles Laughton.

Although this movie is supposed to be based on fact, the scene in which the spy breaks into the Germany Navy code room is fiction. In fact, the British code breakers at Bletchley Park had already broken the German codes and knew how to pinpoint Atlantis. However, to keep the Germans from knowing this, various cover stories were invented during the war. This error is not the fault of the film makers as this information wasn't revealed to the general public until 1974, 14 years after this movie was made.

Opening credits prologue: HOWEVER INCREDIBLE THEY MAY SEEM THE EVENTS NARRATED IN THIS PICTURE ACTUALLY OCCURRED