Marine Sergeant James O'Hearn is being tried at the San Diego Marine base for desertion, theft, scandalous conduct and destruction of property in time of war. He refuses to testify or plead guilty or not guilty to the charges. Showgirl Ginger Martin takes the stand against his protest. She testifies O'Hearn won't talk because he is protecting the name of his pal, Marine Private Davey White. Ginger tells how she, broke and stranded, met the two marines in Shanghai two weeks before Pearl Harbor.

The US Army has decided to modernize its cavalry, so Colonel James E. Devers is ordered by a general to convert a horse unit to motorcycles, but his men are easily outclassed as riders by a pack of rowdies, especially Grady Westfall; when he is arrested risking a long jail term, he's given one way out: enlisting as Corporal, assigned as driving instructor. Unit commander Captain Jack Hassler reviles his unorthodox boyish methods as undermining discipline and tradition, not to mention flirting with the Colonels daughter Beryl Ann, but he's needed, especially when his unit is deployed on a secret mission in Spain.

Paddy Doolan refuses to accept change. In a new century where the motor car is changing the way things are done, the stubborn Irishman, the last of the draught-horse teamsters, continues to haul timber the old way.