The Supermarine Seal was an amphibian reconnaissance and fleeting spotting aircraft that served as the prototype for the successful Supermarine Seagull, which was itself the basis of the more famous Supermarine Walrus.
The Seal was based on the Commercial Amphibian, R. J. Mitchell's first design for Supermarine. This had a boat like prow and a two-step hull. Two passengers could be carried in a covered cockpit in the forward fuselage, with the pilot's open cockpit behind. It was powered by a pusher engine and had folding biplane wings. The aircraft was produced to compete for an Air Ministry Civil Aeroplane Competition of 1920.
The Air Ministry examined the Commercial Amphibian (possibly giving it the name Seal I), and then ordered a single prototype of an improved model as the Seal II (N146). The Seal II was also designed by R.J. Mitchell.
This aircraft was a two bay biplane, with rear folding wings, and wing tip floats mounted under the outer wing struts. It was powered by a 450hp Napier Lion IB, which was mounted between the wings (nearer to the upper wing), and used in a tractor configuration. The wooden fuselage had an oval cross section and two steps underneath.
The main wheels could fold partly up when not needed, taking up a position that put them above the water line. The tail skid also served as a rudder.
The pilot sat in an open cockpit in front of the wings. The wireless operator was positioned just behind the wings.
The Seal II carried a single machine gun in the pilot's position and there was a second machine gun in a dorsal position.
The Seal II made its maiden flight in May 1921. It was tested at Grain in June 1921, and as a result of these tests the fin and rudder were redesigned.
The Seal II was further modified to satisfy Air Ministry Specification 7/20, and in July 1921 it was renamed as the Seagull I. This became the first of a successful family of amphibians, ending with the Seagull V, which was then renamed as the Supermarine Walrus. That version of the aircraft saw extensive service during the Second World War.
Engine: Napier Lion IB or Napier Lion II
Power: 450hp or 480hp
Height: 14ft 10in
Empty weight: 4,100lb
Max speed: 112mph
Endurance: 4 hours
Armament: Up to two .303in Lewis guns