After Lord Trenchard retired in 1929 his successors had to fight to keep the RAF separate from the Royal Navy and the British Army, but Trenchard's foundations proved solid.
By the time World War II broke out in 1939, the then occupant of the post, Air Chief Marshal Sir Cyril Newall, had a service that had been undergoing the most rapid of expansions during the British rearmament programs of the late 1930s. Newall gave way in 1940 to Air Chief Marshal Sir Charles Portal, who led the service for the rest of the war. Portal was a tireless defender of the RAF and extremely able in administration and strategy.
Postwar the RAF was reoriented to perform the dual roles of defending the shrinking British Empire and possibly fighting against the Soviet Union in a Warsaw Pact verses NATO war over Germany and the United Kingdom. The Chiefs of the Air Staff of the day had to fight a constant battle to keep the British aircraft industry alive. In the end only minimal success was achieved, with only a rump aviation industrial base left by the 1970s.
^ The ranks shown are the highest rank that the officer in question attained during his tour as Chief of the Air Staff. However, in the case where the officer was promoted on the day before he was posted, then the lower rank is shown.