Actually the Marine Corps had "Flying Sgts" in WWII and into the Korean War.
Example:
Lawrence County News December 14, 1950
M/Sgt Hugh Newell killed in Korea
M/Sgt Hugh Newell, son of Mrs. Edna Newell, 1111 Tenth Street, Lawrenceville, was killed in action in Korea on December 7,according to information released by the War Department. Newell was a flying sergeant with the Marine Air Force, piloting a Corsair Fighter plane.