Snuffy Smith (Bud Duncan), moonshining hillbilly, grows tired of dodging revenue agents, headed by Cooper (Edgar Kennedy), and decides to take the army up on their offer of free clothes, food and $21.00 a month. Once enlisted, he finds that revenue agent Cooper is his sergeant. Don (Jimmie Dodd), a hillbilly soldier friend of Snuffy, has invented a range finder, but it is stolen by some fifth columnists and hidden in Snuffy's bag. Snuffy decides he has all the army discipline he cares for and heads back to Smokey Mountain, followed closely by the enemy agents.

Hillbilly Snuffy Smith operates an illegal distillery near his home in the Smoky Mountains, and spends most of his time defending the still from revenuer Cooper. Snuffy decides to enlist in the Army when he learns from his cousin Don that the Army pays for food, clothing and shelter. However, he is rejected because he is too short. When Snuffy saves an Army general from being run over by a runaway motorcycle, the general sends his sergeant, Cooper, to thank Snuffy. Snuffy's industrious wife Lowizie, meanwhile, has concocted a liquid that makes everything it touches invisible. Snuffy uses the brew on his dog, Mr. Carson, and the invisible Mr. Carson accompanies him back to the camp with Cooper. The general demonstrates his appreciation by making Snuffy the camp servant, or "yardbird" under Cooper's command. After Cooper shows the general Don's improved range finder invention, the general decides the instrument will help him win the next maneuver test. Later, the general reluctantly dismisses Snuffy because he does not follow Army discipline. Shortly after, a spy infiltrates Cooper's office, steals the range finder, and hides it in Snuffy's duffel bag. Snuffy unwittingly accepts a ride from the spy's attractive comrade, but runs away when she assaults him. After they are relocated to the Smoky Mountains, the general sends for Snuffy to help him with maneuvers. Although Snuffy complies, his friends and family are disagreeable, and fire at the soldiers, whom they assume are revenuers. When Cooper agrees to drop the charges against the hillbillies if Snuffy destroys the still, Snuffy convinces his friends to fight for the general. During maneuvers, the general is hit by a flour bomb, which signifies that he has been "killed" in action, and Cooper and Snuffy are left to command the troops. Lowizie and her cousin, Cindy, meanwhile, take the spies hostage after another attempt to steal the range finder. Lowizie then marches her hostages to Snuffy, who uses the range finder to win the maneuvers. Cindy's previously secret engagement to Don is then sanctioned by her father Saul, who had been feuding with Don's family, but impressed by Don's invention, Saul calls a truce.