The Napier Lion was a broad arrow-style W12 engine produced by Napier at Acton, West London, from 1917 to the late 1930s. This mostly alloy engine had a capacity of litres (cu in) and produced from . It was used in many racing cars by John Cobb and Malcolm Campbell, racing aircraft such as the Supermarine S.5 Schneider Cup winner, and speed boats such as Hubert Scott-Paine's Miss Britain III.