Joined the RAF's Physical Laboratory at Farnborough in 1915, developing a theory of recovery from an aircraft spin and learning to fly in order to test his theory on himself. Appointed Professor of Experimental Philosophy at Oxford, in 1919 (and again, 1953-1956), and acted as scientific adviser to Churchill during the 1930's. Became Churchill's personal assistant from 1940 and also served as Paymaster-General from 1942-1945 and 1951-1953; advocate of the strategy of area bombing German cities during the war.