Early in the First World War, Napier were contracted to build aero engines to designs from other companies, initially a
Royal Aircraft Factory model and then
Sunbeams. Both engines proved to be unreliable and in 1916 Napier decided to design an engine with high power, light weight and low frontal area. Napier's engineers laid out the engine with its 12 cylinders in what they called a
"broad arrow"—three banks of four cylinders sharing a common crankshaft. The configuration is also known as a
W engine. The engine was also advanced in form, the heads using four valves per cylinder with twin overhead
camshafts on each bank of cylinders and a single block being milled from
aluminium instead of the common separate-cylinder steel construction used on almost all other designs. In contrast to the long stroke small bore engine designs typical of the period, the Lion engine was also well ahead of its time in being
oversquare, the cylinder bore diameter being larger than the crankshaft stroke, this allowing higher engine speeds and greater efficiency. arrangement Under
Arthur Rowledge, the design of the engine, renamed Lion, was completed in 1917; hand-built prototypes ran later that year. It was fitted to an
Airco DH.9 in early 1918, and many cooling problems were observed during testing. The milled block was difficult to build with the required accuracy and the design reverted to separate aluminium cylinders. Both problems were solved by the middle of the year and the engine entered production in June 1918. The first Lion I versions delivered from their 24
litres. The power output made the Lion the most powerful Allied aircraft engine, which had previously been the
Liberty L-12, producing . As the most powerful engine available (particularly after a
turbocharger became an option in 1922), the Lion went on to commercial success. Through the years between the wars the Lion was ubiquitous and Napier manufactured little else. They stopped making cars in 1925 and little thought was given to replacing their world-famous product. Between the wars the Lion engine powered over 160 different aircraft types. car In
highly tuned racing versions, the engine could reach and it was used to break many world height, air speed and distance records in aircraft and boats, delivering in a highly tuned Lion for a water speed record of in 1933. In land speed records, Lion engines powered many of
Sir Malcolm Campbell's
record breakers including a record of over in 1932 and
John Cobb's
Railton Mobil Special in 1947—a record that came well after the Lion had passed its prime and stood until the 1960s. The record had been held by British drivers for 32 years. Lions powered successful entrants in the most prestigious event in air racing, the
Schneider Trophy, in 1922 and 1927 but were dropped by
Supermarine in favour of a new engine, the
Rolls-Royce R, which had been designed for racing. During the 1930s a new generation of much larger and more powerful engines appeared and the Lion became uncompetitive. By the time the
Bristol Hercules and the
Rolls-Royce Merlin arrived in the late 1930s, the Lion was obsolete. The Sea Lion, a marine version of the Lion, was used to power high speed
RAF Rescue Launches. The Lion aero engine was also adapted to power
aerosledges, which were used for high-speed transport and SAR duties on sea ice by the
Finnish Air Force and Navy. Turning away from the broad arrow layout, Napier designed new engines using the more compact
H engine layout. The 16-cylinder
Napier Rapier produced and the 24-cylinder
Napier Dagger delivered just under . The engines were smaller than contemporary designs from other companies and Napier started afresh with a new
sleeve valve design, which evolved into the
Napier Sabre. ==Variants==