Leave It to the Marines (1951)

Gerald Meek and Myrna McAllister go to city hall to apply for a marriage license. Gerald wanders into the Marine Recruiting office by mistake and Sergeant Delaney signs him into the Marine Corps and sends him for a medical examination before Gerald realizes what has happened. He finds himself in uniform and ready to be shipped to boot camp without any delay, other than explain to his intended-bride that Uncle Sam has other plans for him.