Which airplane visionary advocated for an independent Air Force and was court-martialed by President Coolidge?

The visionary who advocated for an independent Air Force and faced court-martial by President Coolidge was Colonel William "Billy" Mitchell. He is recognized as one of the pioneers of military aviation and a strong proponent for the development of airpower as a key element of military strategy. Mitchell believed that air power could dominate the battlefield and argued passionately for the establishment of an independent air service separate from the Army and Navy.

His aggressive stance on airpower led him to conduct several public demonstrations to showcase the potential of aviation in warfare, including notable events where he sank decommissioned ships using bombers. His outspoken criticism of military leadership and processes ultimately culminated in his court-martial, where he was charged with insubordination. Despite being convicted, Mitchell's efforts contributed significantly to the eventual creation of the United States Air Force as a separate branch of the military in 1947.

Other figures listed, such as Colonel Jimmy Doolittle, General H. H. Arnold, and Colonel George C. Kenney, played important roles in the history of U.S. airpower, but none were court-martialed over the issue of air force independence nor advocated for it in the same prominent way as Billy Mitchell did.