During World War II, Chief Aviation Pilot Ned Trumpet, jokingly called "Old Gas Bag" by some of his Navy pals, handles his lighter-than-air airship with ease as he and his crew make a difficult landing at the fog-enshrouded Lakehurst, New Jersey airfield. Ned, who often brags about his flying capabilities and is known to embellish his war stories, makes up one of his biggest lies when he tells his friends that he has a son. After recounting numerous stories about his "son," and insisting how proud he is of the boy, Ned panics, realizing that he will someday be expected to introduce his pals to hin. Ned finds the perfect young man to impersonate his son on the day that he falls from a hot air balloon and parachutes into a ranch owned by Maude Weaver. Maude lives with her son Jess, who is fascinated by Ned's flying stories. Before returning to his base, Ned suggests that the young man join the lighter-than-air service, unaware that Jess has a physical disability. Back with his flying buddies, Ned resumes his storytelling, referring to Jess as "his boy," and eagerly awaiting the day when he will be able to show him off. Although Ned soon discovers that Jess is disabled, he is determined to instill faith in the boy and help him realize his dreams. Ned arranges an operation to correct the problem with Jess's legs, and the operation is a success. Afterward, Ned proudly introduces his "son" to his pals, and though Ned has not told Jess about his lie, Jess goes along with the ruse. To Ned's delight, Jess lives up to his expectations and soon earns his flying license. One day, while on a submarine patrol mission, Ned becomes overly anxious to see Jess execute his first bombing, and orders an unauthorized and premature attack on a Japanese submarine. Jess's bomb misses its target, however, and when the submarine fires back, the airship is hit. Ned quickly takes over the controls and sinks the submarine, but, in the aftermath of the skirmish, Jess finds himself facing a court-martial for disobeying orders. The situation looks bad for Jess until Ned steps forward and takes the blame for his actions. When Jess later rejects Ned's friendship and asks to be transferred to the Ferry Command, Ned takes the request as an insult and ends his friendship with the young man. Some time later, while on assignment in Burma, Ned is visited by Jess, who has volunteered to fly a dangerous mission across enemy lines. Ned is still hurt by Jess's rejection, but when Jess's plane crashes in Japanese territory, he rushes to the scene with a rescue team. Both Ned and Jess emerge safely from the jungle and are reunited on a transport ship returning to the United States. In Lakehurst, Ned and Jess are decorated for their heroism, after which Jess indicates that he will be returning to the lighter-than-air service.