Became its own branch under the National Security Act of 1947
TABLE OF ... 
United States Marine Corps), and the Air Force, with their assigned combat and 
service ... Defense, appointed under section 202; the Secretary of the Army, 
referred to in section ... Department of the Air Force, or any branch, bureau, unit 
or division... [DOC] [TLE] The U.S. Air Force Birthday | Military.com [PAR] 1947 -- The U.S. Air Force Gains its Independence ... the Air Force ended a 40-
year association with the U.S. Army to become a separate service.