Napier-Halford Dagger Series II, H-24 Engine

Type: Reciprocating, 24 cylinders, Air cooled, Supercharged

Power rating: 470 kW (630 hp) at 3,500 rpm

Displacement: 16.8 L (1,027 cu in)

Bore and Stroke: 96.8 mm (3.8125 in.) x 95.3 mm (3.75 in.)

Weight: 587 kg (1,295 lb)

Frank B. Halford was a talented independent British engine designer of the early and mid-twentieth century who worked for a number of manufacturers including de Havilland, Cirrus and Fiat. In 1928, he contracted with Napier for design of a series of air-cooled engines in a vertical H configuration having twin crankshafts geared together. There were two basic types, the 16-cylinder Rapier and the 24-cylinder Dagger. The Rapier, produced in small numbers, powered the Short Mercury seaplane. By 1935, the Dagger served a large military market, and the British Air Ministry ordered it in quantity. Both the lower powered Dagger I and Dagger II versions powered the Hawker Hart aircraft. The final version, the 712 kW (955 shp) Dagger VIII, powered the Fairey Battle I and Handley Page H.P.52 Hereford I.

Late in his career, with access to the work of Frank Whittle, Halford led the de Havilland Engine Co. where he designed turbine engines.