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Napier Lion W-12 Engine


Display Status:

This object is on display in the Boeing Aviation Hangar room at Steven F. Udvar-Hazy Center in Chantilly, VA.

Napier Lion W-12 Engine

Collection Item Summary:

With an industrial history dating to the early nineteenth century, D. Napier and Son began building aircraft engines in the World War I era. Napier began work on a remarkable new engine, the Lion, in 1916. Its three banks of four cylinders formed a "W" or "Broad Arrow" configuration. The arrangement provided a much shorter crankcase, a stiffer and simpler crankshaft, and a more compact engine than the 12-cylinder "V" construction of other high-performance engines of the period. Napier produced the reliable and widely used Lion series from 1917 until 1932 for military, commercial, and special-purpose racing aircraft.

This early version of the Napier Lion is believed to be a Model II or IIB. Napier manufactured these models from 1918 through 1925 to power many British aircraft types, including the Handley Page H.P.15 V/1500 bomber, Supermarine Sea Lion I racer, and the Felixstowe F.5 flying boat.

Collection Item Long Description:

Data Source

National Air and Space Museum


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


A. J. Rowledge

Credit Line

Transferred from the U.S. Navy, Naval Supply Center, Cheatham Annex, Williamsburg, Virginia.


Length 125.7 cm (49.5 in.), Width 106.4 cm (41.9 in.), Height 91.4 cm (36.0 in.)

Country of Origin

United Kingdom



Physical Description

  • Type: Reciprocating, W-type, 12 cylinders, liquid cooled
  • Power rating: 336 kW (450 hp) at 1,925 rpm
  • Displacement: 24 L (1,462 cu in)
  • Bore and Stroke: 140 mm (5.5 in.) x 130 mm (5.13 in.)
  • Weight: 389 kg (858 lb)


PROPULSION-Reciprocating & Rotary

Inventory Number