Up Periscope!

James Garner, in one his earliest starring roles, is Lt. J.G. Kenneth M. Braden, an elite U.S. soldier during World War II. After being reluctantly pulled away from a week-long romance, Braden is given the dangerous mission of infiltrating a Japanese-held island. He must scuba ashore, and alone behind enemy lines, capture a top secret radio code before escaping to an awaiting U.S. submarine.