Napier Sea Lion Engine


Restoration I

Restoration II

Restoration Description:

Details Awaited


Napier entered the aero-engine business in WW1, building engines designed by the Royal Aircraft Factory at Farnborough and later Sunbeam. Napier, in 1916, designed their own broad arrow design engine that was to be called the Lion that just missed war service. Napier strived for high power to weight and minimal frontal area and achieved this by having three banks of four cylinders. The resulting three bulges in the engine nacelle characterised its installations. Each cylinder had two inlet and two exhaust valves operated by double overhead camshafts for each of the three banks, which are described as 'broad arrowhead' form. By 1922 the engine was fitted with exhaust driven superchargers (turbochargers) which significantly improved performance especially at high altitude.

The Napier Lion may be the most widely used and successful aircraft engine ever built. It powered more than 160 types of aircraft worldwide (including Germany, Italy, Russia and Japan), it set world speed records in the air, on land and on water.

The world record breaking history of the Lion is remarkable, at least 9 world records over a 28 year history.

1919 Height Record of 30,500 feet.
1929 Land Speed Record at 231.3 miles per hour.
1929 Air Speed Record at 336.3 miles per hour.
1930 Water Speed Record at 100.13 miles per hour.
1931 Land Speed Record at 246.1 miles per hour.
1932 Land Speed Record at 253.968 miles per hour.
1933 Air long Distance Record at 5,309 miles.
1939 Land Speed Record at 369.74 miles per hour.
1947 Land Speed Record at 394.196 miles per hour.

Names such as Campbell, Seagrave and Cobb are prominent as the record setters in the above list.

The air racing history includes the Schneider Trophy races : 1922. Held at Naples, Italy. 1st place in a Supermarine Sea Lion II with a 456hp Napier Lion engine at a speed of 145.7 mph (234.48 km/h). 1923. Held at Cowes, Isle of Wight. 3rd Place, a Supermarine Sea Lion III with a 525hp Napier Lion III. 1925. Held at Baltimore, Md., USA. 2nd place in a Gloster III, Napier Lion VII of 670hp, a speed of 225mph (362km/h). 1927. Held over the Solent. 1st and 2nd places, Supermarine S5 with a 874hp Napier Lion VIIB engine at a speed of 281.68 mph (453.22 km/h). 1929. Held over the Solent. 3rd place, a Supermarine S5 with a 874hp Napier Lion VIIB engine at a speed of 282.15 mph (454.02 km/h).

A total of at least 9 race starters were powered by Lion engines from 1919 to 1929 when Rolls Royce finally eclipsed the Lion, this was RR's only competitive win as in '31 there were no other entries due to pre race tragedies (by contrast, in 1924 the competition had withdrawn after the British entry crashed).

The "Sea Lion" was intended for maritime use in high performance boats and it might seem odd that the museum is refurbishing this version of the Lion. There is actually one use that makes it very appropriate that it is being restored by an aviation museum. This engine was used in the type 100 High Speed Launches designed by the British Powerboat Company which were fast long range offshore rescue craft. Each 64 foot long launch used three of these engines to deliver 1500 hp and obtain a speed of 45 mph, a good performance even today. One of these launches, HSL 102, has been restored by the British Military Powerboat Trust (Marchwood, Southampton). In the month of June 1941 alone, this one boat rescued 38 RAF airmen.


With such a long and varied life the engine cannot be represented by one simple set of data. The following figures are a reasonable summary however:

Type: W12 spark ignition natural aspirated 4-stroke piston engine

Cylinders: 3 in 60 angle rows

Valve arrangement: 4 poppet valve in each cylinder

Bore and stroke: 5.5 x 5.125 in

Swept volume: 1461 cu in ( 23.9 litre)

Compressions ratio: 5.5:1 to 10:1 on racing engines

Max revolution: 2200

HP range: 468 - 1320

Weight, lbs: 930



The APSS is a registered charity in Scotland, charity No. SC033307
A member of the British Aviation Preservation Council