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. One especially notable application was the Supermarine S.5, which, powered by a 656 kW (880-hp) Lion VIIB engine, won the Schneider Trophy Race in 1927.

Although the Lion became uncompetitive for aviation after 1930, the Sea Lion marine version stayed in production for RAF rescue application until 1943.