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Note: This is a sub-section of Napier
1921 By an arrangement between the Air Ministry and de Havilland, Major Frank Halford, working as a consultant, designed the 16-cylinder air-cooled Rapier, and this was followed by the compact Napier-Halford Dagger engine, which had 24 cylinders in H-form (four banks of 6 inline cylinders).
The Dagger was intended to power a small, highly aerodynamic fighter aircraft. The intended size of the aircraft favoured the adoption of an air-cooled inline engine, and considerable effort was devoted to the ducting of cooling air. The 24-cylinder 1027 cu in (16.84 litres) engine developed 635 HP in 1934, and was cleared for production in 1936, developing 1000 HP at the high speed of 4200 rpm. A version was bench-tested at 1500 HP. However, the fighter did not materialize, and the engine was misapplied to a bomber, the Handley Page H.P.53 Hereford .