Who was an early proponent of military aviation, calling for an independent Air Force?

The correct choice highlights Colonel William "Billy" Mitchell as a key figure in advocating for military aviation and the establishment of an independent Air Force. Mitchell was an early and vocal supporter of the potential for air power in warfare, emphasizing its strategic importance and the necessity for a separate branch of military service dedicated solely to aviation. He believed that air power could be a decisive factor in combat and argued passionately for the creation of a distinct Air Force that would operate independently from the Army and Navy. His extensive efforts, including public speeches and demonstrations, helped lay the foundation for future developments in U.S. military aviation and ultimately influenced the establishment of the U.S. Air Force in 1947.

The other individuals listed made significant contributions to military aviation and leadership in various capacities but did not advocate as strongly or singularly for an independent Air Force as Mitchell did. Their roles were impactful yet did not carry the same pioneering spirit seen in Mitchell's actions and beliefs.