R.J. Mitchell, who later designed the Spitfire, joined Supermarine in 1917. A racing design, the Sea Lion was developed from an earlier aircraft designed to meet an Admiralty experimental requirement to compete in the 1919 Schneider Trophy race, but was badly damaged by an underwater obstruction. Undeterred, Mitchell went on to redesign the Sea Lion (II) biplane flying boat (itself a derivative of the Sea King fighter), powered by a strut-mounted single pusher engine. The new Sea Lion won the 1922 Schneider race in Naples. The Sea Lion (III) was fitted with an uprated engine for the 1923 event at Cowes, but only managed third place. Mitchell was well aware of the need to decrease drag and moved on to design the S.IV.