The Napier Lion was a 12-cylinder broad arrow configuration aircraft engine built from 1917 until the 1930s. A number of advanced features made it the most powerful engine of its day, and kept it in production long after contemporary designs had stopped production. It is particularly well known for its use on a number of racing designs, in aircraft, boats, and cars.

Used in: "Golden Arrow" (car and boat); "Blue Bird" (1927 and 1931); Miss England I; Supermarine S.4 and S.5; Gloster IV; Gloster Guan; Gloster III (Schneider Trophy entrant); Miss Britain III; Gloster VI (Schneider Trophy entrant); Railton Special (land speed record car); Gloster Gorcock; Napier-Railton; British Power Boat Company Type Two 63 ft HSL (Sea Lion, marine version); and private crafts.