As early as 1938 Roy Fedden, who designed most of the Bristol Engine Company's most successful aero engines, pressed for the introduction of 100 octane aviation fuel from the US, and later that year the British aero engine manufacturers Bristol and Rolls-Royce demonstrated variants of their 'Mercury' and 'Merlin' engines rated for 100 octane fuel. A memorandum by the "Department of Defence Co-Ordination", 'Proposals for securing adequate supplies of 100 octane fuel to meet war requirements', 23 December 1938, noted that there was a need to increase supplies of 100 octane fuel and discussed ways in which this could be achieved.