In 1942, during a court-martial trial at a Marine Corps base in San Diego, Sgt. James O'Hearn stands mute when charged with desertion, stealing a yacht, sinking a saloon, shanghaiing sailors and scandalous conduct. The first witness to testify is Orville H. Masterson, a Navy boatswain's mate who first spotted O'Hearn and a showgirl, Ginger Martin, floating on a raft near Guadalcanal. Masterson claims that O'Hearn, who was near death and delirious when found, raved that he and his buddy destroyed the Japanese Navy single-handedly. Over O'Hearn's mysterious objections, Ginger testifies next, detailing how she became stranded in Shanghai two weeks before Pearl Harbor was bombed: To earn passage money home, she takes a job in a waterfront saloon. When the Marines are suddenly ordered to pull out, her free-spirited friend, Pfc Davey White, offers to marry her so that she can be evacuated with the military families, but wanting her for himself, her boss Fatso fights Davey. Then the straitlaced O'Hearn shows up looking for Davey, and the three escape in a motorboat. However, they fail to untie the boat from a support beam and pull the saloon into the river. O'Hearn, who has been Davey's mentor, is anxious to drop off Ginger and rendezvous with the Marines, but Davey wants to get married first. They argue, fight and accidentally break the steering mechanism on the boat. As they drift helplessly out to sea, Wu Ching and his family rescue them. O'Hearn pays Ching to take his junk back to Shanghai, but they continue on course in the opposite direction. Meanwhile, Davey wants Ching, as ship's captain, to perform a marriage ceremony. Resenting how Davey has changed since meeting Ginger, O'Hearn maliciously teases her that real Marines like Davey are fickle, then bribes Ching to perform a burial rite instead. Davey fights O'Hearn again, and their pranks cause a ship fire. Ching banishes them at gunpoint, and they swim to the shore of the Vichy French island of Namou. There they sense anti-American sentiment and learn that Pearl Harbor has been bombed, so to avoid being imprisoned with Free Frenchmen in the dungeon, O'Hearn and Davey claim to be deserters. Back in the courtroom, the former governor of Namou, Pierre Marchand, testifies that he believed them to be deserters and introduced them to Mme. Lily Duval, owner of Namou's hotel. As further proof of O'Hearn's desertion, Lily is called to the stand and testifies that everyone on Namou is a deserter of either a wife or girl friend. The next day, Ginger is recalled and continues the story: While she and Davey wait for the island priest to marry them, a Dutch yacht unexpectedly docks. Its captain, Van Dorck, whom O'Hearn overhears speaking German to Marchand, refuses to take passengers. O'Hearn makes plans to steal the yacht with the help of an old sailor, Jimmylegs Donovan, but cannot enlist Davey's help, as he has decided to desert. In the courtroom, Ginger says that, if Davey were with them, he would be the one on trial. O'Hearn testifies just before closing arguments, as he wants to keep Davey's record unblemished: After realizing that Van Dorck is really a German delivering radar equipment to islands near Guadalcanal, O'Hearn and Jimmylegs liberate the island prisoners, steal arms and ammunition hidden in the dungeon and recruit a crew. O'Hearn kidnaps Davey during his tribal wedding ceremony and after "requisitioning" the yacht, the crew sails toward Guadalcanal, where, O'Hearn has learned, the Marines are fighting. At sea, O'Hearn discovers that Ginger has stowed away, but a Japanese fleet of landing barges and a destroyer captures his attention. Flying a Dutch flag, the yacht gets close enough to the destroyer to shoot out its steering mechanism, gunnery control and intercom. Most of the motley, but resourceful crew dies during the ensuing battle. When the destroyer is within a few feet of the yacht, Davey, having regained his fighting Marine spirit, jumps aboard and, after a final salute, drops dynamite into the smokestack. To conclude his testimony, O'Hearn explains that he and Ginger, the only survivors, abandoned ship and were later rescued by the Navy. O'Hearn adds that Marines are special and crazy, and pleads that they leave Davey on the honor roll. Later, O'Hearn, who has been cleared of all charges, tells Ginger that Davey has been awarded a posthumous Congressional Medal of Honor and then proposes to her.