The first aircraft to be designed by Supermarine's Reginald Mitchell, it was built at the company's works at Woolston, Southampton, for an Air Ministry competition that took place during September 1920.

The Commercial Amphibian finished second in the competition, but was judged the best of the three entrants in terms of design and reliability, and as a result the prize money of £4,000 (equivalent to £193,010 in 2023)[1] was doubled.

The aircraft had to be able to fly 350 nautical miles (650 km; 400 mi) at 300 metres (980 ft) at a speed of at least 70 knots (130 km/h; 81 mph), whilst carrying a minimum load of 230 kilograms (510 lb).

[4][5] The front of the aircraft was designed to make sure that it lifted clear of the water prior to take-off, and the nose profile was similar to that of a boat.

[10] Because of its larger weight and slower speed in comparison with its two competitors, the Supermarine Amphibian performed poorly in the air, but it was judged to be the competition's best constructed and most reliable aircraft.

The Amphibian's consolation prize of £4,000 was doubled to £8,000 (equivalent to £386,020 in 2023)[1] by the Air Ministry, which judged Mitchell's design to be excellent and the aircraft to have performed well, considering that it had the lowest powered engine of the three competitors.

[7][11] The Commercial Amphibian crashed a month after the competition,[12] when on 13 October 1920, after departing from Southampton, it was involved in an accident at Great Bookham, Surrey.

[15] Features seen in the Amphibian were later used to develop the Supermarine Walrus, hundreds of which were built and were in operational service throughout the World War II.