Napier-Halford Dagger Series II, H-24 Engine


Display Status:

This object is not on display at the National Air and Space Museum. It is either on loan or in storage.

Collection Item Summary:

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.

Collection Item Long Description:

Data Source

National Air and Space Museum

Restrictions & Rights

Do not reproduce without permission from the Smithsonian Institution, National Air and Space Museum

Credit Line

Transferred from the U.S. Navy


Steel, Paint, Aluminum, Magnesium, Wood, Stainless Steel, Rubber, Copper


Height 175.3 cm (69 in.), Width 99.1 cm (39 in.), Depth 223.5 cm (88 in.)

Country of Origin

United Kingdom


Circa 1938

Physical Description

  • 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)


PROPULSION-Reciprocating & Rotary

Inventory Number