In 1915 Henderson returned to London to resume his London-based duties as director-general of military aeronautics, which Sefton Brancker had been performing in his absence. This meant that when, in 1917, General Jan Smuts was writing his review of the British Air Services, Henderson was well placed to assist. While seconded to General Smuts, Henderson wrote much of what came to be called the Smuts Report. It has been argued that he had a better claim to the informal title "father of the Royal Air Force" than Sir Hugh Trenchard. Trenchard himself believed that Henderson deserved the accolade. He sat on the government's "Advisory Committee for Aeronautics", located at the National Physical Laboratory, under the chairmanship of Richard Glazebrook and presidency of John Strutt, Lord Rayleigh.
