A number of advanced features made it the most powerful engine of its day and kept it in production long after other contemporary designs had been superseded.

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.

Under Arthur Rowledge, the design of the engine, renamed Lion, was completed in 1917; hand-built prototypes ran later that year.

The milled block was difficult to build with the required accuracy and the design reverted to separate aluminium cylinders.

In highly tuned racing versions, the engine could reach 1,300 hp (970 kW) and it was used to break many world height, air speed and distance records in aircraft and boats, delivering 1,375 hp (1,025 kW) in a highly tuned Lion for a water speed record of 100 mph (160 km/h) in 1933.

The Lion aero engine was also adapted to power propeller-driven motor sleighs, which were used for high-speed transport and SAR duties on sea ice by the Finnish Air Force and Navy.