was then posted to the Philippine Air Depot, where he served at various times as property officer, supply officer, adjutant, and depot inspector, before ultimately being assigned to the 28th Bombardment Squadron in 1924. In August 1923 he crashed an Airco DH.4 on takeoff but walked away unhurt. The Walkers had two sons, Kenneth Jr., born in February 1927, and Douglas, born in January 1933. 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. One of Walker's tasks was to rewrite the bombardment text. He felt it was flawed because it failed to drive home what he saw as the most important fact, that "bombardment aviation is the basic arm of the air force". Following the views of air power theorists Billy Mitchell, Hugh Trenchard, and Giulio Douhet, Walker enunciated two fundamental principles: that bombardment would take the form of daylight precision bombing; and that it should be directed against critical industrial targets. In his article "Driving Home the Bombardment Attack", published in the Coast Artillery Journal in October 1930, he argued that fighters could not prevent a bombing attack and that "the most efficacious method of stopping a bombardment attack would appear to be an offensive against the bombardment airdrome." The Bomber Mafia argued that bombers flew too high and too fast to be intercepted by fighters, that even if they were