The Andy Griffith Show

Gomer decides to join the Marines, and Andy helps out by secretly convincing the drill instructor that Gomer is the son of a decorated general. The drill instructor takes Gomer under his wing and gets him to pass his inspection with flying colors, only to find out later the truth behind Gomer's lineage. (Pilot episode for the spin-off series "Gomer Pyle, U.S.M.C.")