The HG Hawker Demon was a two-seat fighter derivative of the Hawker Hart day bomber. It was designed against Specification 15/30, which was drawn up around the performance of the existing Hart design by Sydney Camm.
H.G. Hawker modified the first production Hawker Hart (J9933) to act as a prototype Hawker Demon although it was originally known as the Hawker Hart Fighter. The main changes from the Hart were the use of a 560 hp supercharged Rolls-Royce Kestrel V(DR) engine and a downward sloping rear cockpit coaming, which afforded a better field of fire for the rear gunner. Two fixed forward-firing Vickers machine guns were fitted in troughs on either side of the fuselage. Under-wing racks could also be fitted for the carriage of light bombs as required.
The first batch of Hawker Hart Fighters were supplied to 23 Sqn RAF in May 1931. Production Hawker Demon aircraft (to Specification 6/32) were supplied initially with the 485 hp Rolls-Royce Kestrel IIS, with later machines having the 585 hp Rolls-Royce Kestrel V. The first production Hawker Demon (K2842) was first flown on 10th February 1933. Difficulties with the slipstream affecting the performance of the rear gunner, resulted in a segmented, hydraulically-operated retractable windshield (built by British sports car manufacturers Frazer Nash) being fitted to all later Hawker Demons. These aircraft were sometimes known as 'Turret Demons'.
In addition to use by the RAF, 64 Hawker Demon aircraft, with a 600 hp Rolls-Royce Kestrel V(DR) engine, were supplied to the Royal Australian Air Force (RAAF). These aircraft were used for general purpose, army co-operation and training duties, rather than exclusively as fighters. They were also equipped with a tailwheel, rather than a tail skid undercarriage.
A total of 304 Hawker Demon aircraft were built, comprising one prototype, six Hawker Hart Fighters, 233 Hawker Demons for the RAF and 64 for the RAAF.
Of the production machines, H.G. Hawker built 133 Hawker Hart Fighters and Hawker Demons for the RAF and all 64 Demons for the RAAF. The remaining 106 Hawker Demon aircraft were built by Boulton Paul Aircraft Ltd. The type remained in limited service with the RAF after the outbreak of the Second World War, being used for roles including target towing.