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Plot

Lt. Kenneth Braden (James Garner), a newly trained U.S. Navy Frogman, is unexpectedly ordered to report for duty without being able to notify his new girlfriend, Sally Johnson (Andra Martin), in whom he has taken a serious interest. He is informed that she is an officer of Naval Intelligence and was responsible for a recent confirmation of his character and fitness for a special mission.

Submarine commander Stevenson (Edmond O'Brien) (whose crew's morale is shaky because of the arguably unnecessary death of a crew member on his last mission) is ordered to take Braden to the island of Kosrae to photograph a code book at the Japanese radio station located there. The skipper originally told Braden that he would have to swim a considerable distance, fighting strong currents, but upon arrival he decides to enter Lelu Harbor and remain there while Braden carries out his covert mission.

After Braden returns, Stevenson dictates a letter accusing himself of putting his submarine and crew in danger in order to make Braden's mission easier. When they reach Pearl Harbor, Braden obliquely informs Stevenson that his crew "lost" the letter. To Braden's surprise and delight, Sally Johnson is waiting at the dock to greet him.