 Walker returned to the United States in February 1925 and was posted to Langley Field, where he became a member of the Air Service Board. He served successively as adjutant of the 59th Service Squadron, commander of the 11th Bombardment Squadron, and operations officer of the 2nd Bomb Group there. In June 1929 he graduated from the Air Corps Tactical School, where he studied under Captain Robert Olds, a former aide to air power pioneer Billy Mitchell and a passionate advocate of strategic bombing. He then served at the Air Corps Tactical School as an instructor under Captain Olds in the Bombardment Section until July 1933, both at Langley and at Maxwell Field, where the school was relocated in 1931. Walker became part of a small clique of Air Corps Tactical School instructors that became known as the "Bomber Mafia", that argued that bombardment was the most important form of airpower. Its members also included Haywood Hansell, Donald Wilson, Harold L. George, and Robert M. Webster, Their influence was such that, during their tenure, bombardment achieved primacy over pursuit in the development of Air Corps doctrine.
