Brigadier General William Mitchell (Gary Cooper) tries to prove the worth of the Air Service as an independent service by sinking a battleship under restrictive conditions agreed to by Army and Navy. He disobeys their orders to limit the attack to bombs under 1,000 pounds from an altitude of greater than 5,000 ft. and instead loads 2,000 pounders. With these, Mitchell directs his aircraft to fly at 2,000 ft. and proves he can sink the ex-German World War I battleship Ostfriesland, previously considered unsinkable. His superiors are outraged.

Politically vocal, Mitchell is demoted to colonel and sent to a ground unit in Texas. A high-profile air disaster occurs in which his close friend Zachary Lansdowne (Jack Lord) is killed, the crash of the dirigible USS Shenandoah. This is followed by a second disaster in which six aircraft flying from a base on the California coast to Fort Huachuca, Arizona, crash. They were poorly maintained because of lack of funds.

Mitchell at this point calls a press conference in which he harshly criticizes the Army. He is then court-martialed. The trial goes slowly for Mitchell's attorney and friend, Illinois Congressman Frank R. Reid (Ralph Bellamy), who tries everything, until he subpoenas President Calvin Coolidge. The court, consequently, decides to adjourn.

Clearly the military wants out of the limelight, but Mitchell refuses to sign a paper Reid has presented him in which he withdraws his criticisms in return for saving his career as an Army officer. Margaret Lansdowne (Elizabeth Montgomery), widow of Mitchell's dead friend from the Shenandoah, then appears in court. The previous barring of evidence demonstrating a justification for Mitchell's criticisms of his superiors failure to develop air power is repealed. Many witnesses are then called forward to corroborate Mitchell's criticisms, including Eddie Rickenbacker (Tom McKee), Carl Spaatz (Steve Roberts), Henry H. Arnold (Robert Brubaker) and Fiorello LaGuardia (Phil Arnold).

Finally Mitchell testifies and is cross-examined by Maj. Allen W. Gullion (Rod Steiger), a prosecutor specially brought in for the job. He stresses that Mitchell had disobeyed his superior officers. Gullion also ridicules Mitchell's attempts at foresight, even when accurately predicting both the Philippines and Hawaii would be attacked by Japan in 1941.

The court finds Mitchell guilty, but he has accomplished his goal of making the public aware of the state of American air power. As his pilots salute him, Mitchell steps out and looks up to see a squadron of four biplanes in flight.