Mystery Sea Raider (1940)

At the outset of World War II, June McCarthy meets Carl Cutler aboard the S.S.Aleria, a British vessel en route to New York from London, where she has been dancing. The ship is sunk in mid-voyage by an unidentified submarine, and Cutler aids in rescuing June. As they arrive safely in Manhattan, June asks Cutler to contact her fiancé, Jimmy Madden, about the use of his stranded freighter, S.S. Apache, in Cutler's import business. By this action, she has unwittingly aided Cutler, who is an undercover Nazi naval officer, with acquiring a mother ship for German submarines in the Atlantic. Cutler charters the Apache and also kidnaps June who, he fears, might realize he was responsible for the sinking of the Aleria. When the ship is at sea, a submarine comes alongside, and the crew climbs aboard to be met by Cutler and his aides in full uniform. Madden is informed that Cutler is now the ship's captain, and then takes the ship on raiding missions in the Caribbean, with Madden and his crew imprisoned in the ship's hold. June is allowed freedom of the ship and Madden believes she is an accomplice of Cutler's. She regains his favor and trust when she conceives the idea of cutting carbide flares from the life preservers for floating S.O.S. messages.