Set on a submarine in the Pacific during World War II, Up Periscope focuses on Lieutenant Ken Braden, a laid-back, inventive and comic Navy man who is assigned to a sabotage mission on a Japanese-held island. But when he discovers that Sally, the woman he's been falling in love with, has been checking out his suspect qualifications to be a US Navy frogman, he must put his personal life behind him and concentrate on the mission at hand.