Although designed around the requirements for the MacRobertson race, owing to its unusual requirements the Comet did not fit the standard technical specification for a racing aircraft, nevertheless it was classed as a "Special, sub-division (f), Racing or Record". De Havilland paid special attention to the non-stop range necessary for the long official stages. They initially intended to produce a twin-engined two-seat development of the DH.71 experimental monoplane. However it would have insufficient performance so the designer, A. E. Hagg, turned to a more innovative design. He chose a modern cantilever monoplane with enclosed cockpit, retractable undercarriage and flaps. In order to achieve take-off at a reasonable speed and with high all-up weight, combined with a satisfactory high-speed cruise, it would be necessary to fit variable-pitch propellers.