Entered for the 1922 Schneider Trophy contest at Naples, Sea Lion II was planned to be able to attain a speed of 160 miles per hour (260 km/h).

Supermarine's test pilot Henry Biard flew the aircraft to victory at an average speed of 145.7 mph (234.5 km/h)—the first post-World War I success by a British aeroplane in an international competition.

[2] Supermarine developed a racing flying boat as a modification of their Sea King II fighter,[3] a single-seat biplane amphibian powered by a 300 hp (220 kW) Hispano Suiza engine in pusher configuration that had first flown in 1921.

[4] Compared with the Sea Lion I, the new aircraft had a more refined hull shape, a differently-designed tail, and a propeller that had four blades, instead of two.

[9] His modifications to the rudder and the fin caused the hull to have to be strengthened by adding an extra layer of varnished fabric stretched around the structure.

[8][9] The Sea Lion II competed against two Italian aircraft, a Macchi S.7 and a Savioa S.19, with two French entrants failing to start the race.