The Supermarine Seal II was a British flying boat developed by Supermarine after it secured a British Air Ministry order for a prototype three seat fleet spotter amphibian.
The prototype, which had to be capable of landing on Royal Air Force (RAF) aircraft carriers, was designed by Supermarine’s R.J. Mitchell, who incorporated suggestions made after the Supermarine Commercial Amphibian achieved second place after it was entered for an Air Ministry competition in 1920.
The Seal II was a biplane with the lower wing mounted on top of the fuselage.
Powered by a 450 horsepower (340 kW) Napier Lion water cooled piston engine, it was the first British flying boat with the propeller positioned in front of the engine.
The pilot was seated forward in the nose with the fuel tanks placed behind him, and a second cockpit was located behind the wing.
The Seal II first flew on 21 May 1921 prior to being assessed by the RAF.
After being modified and fitted with a different engine, it was renamed the Seagull prior to being delivered to the RAF two months later.
In November 1921 the Seal II was one of a number of aircraft sold to the Imperial Japanese Navy Air Service and shipped out with the British led Sempill Mission to Kasuimiguara.