Joseph Carroll (DIA)
When the U.S. Air Force was established as a separate executive department under the National Security Act of 1947, Secretary of the Air Force W. Stuart Symington, requested FBI Director J. Edgar Hoover to loan General Carroll to the services to organize a U.S. Air Force agency for investigative and counterintelligence functions. He organized and directed this new organization, the AFOSI, along the lines of the FBI rather than the U.S. Army's Criminal Investigation Command (USACIDC or CID). General Carroll was tendered a commission as a colonel, U.S. Air Force Reserve, January 12, 1948. He was ordered to active duty in the grade of brigadier general May 6, 1948, and promoted to major general August 11, 1950.
Air National Guard
Being "local" ground forces affiliated with the Army, militias were considered state-centric/territorial-centric in nature, this versus naval forces, which were considered wholly activities of the federal government. This distinction accounts for why there are no National Guard components in the U.S. Navy, U.S. Marine Corps or U.S. Coast Guard. Because the present day U.S. Air Force evolved from the U.S. Army, it was only natural that a separate Air National Guard would be established with the divestiture of the former U.S. Army Air Forces and its establishment as a separate and independent U.S. Air Force in 1947.