Twin sisters Rosemary and Susie Allison are successful nightclub performers. Their act is about to come to a close when serious-minded Rosemary announces she's joining the Waves. Fun-loving Susie decides to enlist also, especially after she learns that crooner Johnny Cabot has just been drafted by the Navy.

Women all over the United States give up their jobs to contribute to the war effort and join the WAVES, the Women's Reserve branch of the Navy. One night, after New York nightclub singers the Allison Twins perform a rousing version of "Join the Navy," Rosemary, the smarter of the pair, tells her dizzy blonde sister Susie that she is tired of just singing the song, and intends to join up. Susie reluctantly enlists with her sister and they join the other recruits at the United States Naval Training School in the Bronx. After five weeks of training, Rosemary and Susie use their night off to see the performance of Susie's heartthrob, singer Johnny Cabot. Rosemary is appalled by the screaming and fainting women who comprise Johnny's audience. Later, at a nightclub, they are introduced to Johnny by their childhood friend Windy, and while Rosemary snubs Johnny because he is still a civilian, Susie faints when she dances with him. Unknown to Rosemary, it is Johnny's fervent wish to follow his father's footsteps in the Navy, but he has been rejected because he is color blind. When the Navy lowers their physical requirements, Johnny enlists and is stationed at the Naval Training Center in San Diego, California, where Susie and Rosemary are also stationed. Windy and Johnny compete for Rosemary's affections, but Rosemary falls in love with Johnny. When Johnny receives orders to ship out on the same ship on which his father served, Susie, unaware of her sister's affection, forges Johnny's name on a letter in which she suggests that Johnny's talents be used to recruit more WAVES. Johnny is mystified when he is then assigned to produce, stage and appear in a theatrical production to recruit WAVES, and angrily blames Windy for keeping him from active duty. To punish Windy, Johnny makes him his assistant, and Windy vengefully convinces Rosemary that Johnny has willfully sidestepped active duty. Susie confides in Windy, who keeps the ruse a secret, and they destroy her original letter. Johnny casts Susie and Rosemary in the show, but Rosemary, now disenchanted with Johnny, drops out and is reassigned to the air traffic control tower. Rosemary changes her mind, however, so that she can convince her infatuated sister of Johnny's cowardice. When Windy learns that Johnny intends to propose to Rosemary, he and Susie formulate a plan in which Susie impersonates her sister, and successfully drives a wedge between Rosemary and Johnny. Disgusted by his situation, Johnny goes AWOL, hoping to rejoin his ship for active duty, but Windy and Susie forestall him, confess the truth, and trick him into missing his plane. Johnny goes on with the show and Rosemary apologizes for the misunderstanding, and is then responsible for Johnny's reassignment to his ship. After Susie discovers there is no "magic" to kissing Johnny, he reunites with Rosemary. Susie then kisses Windy farewell, and faints.