Powered by a Rolls-Royce Griffon engine, it had a radical new wing design to allow safe operations at higher speeds and incorporating inwards-retracting undercarriage.

The Spiteful was ready for production as the war was ending but in testing had shown only marginal improvements over existing types and was now being overtaken by jet-powered designs.

[3] It became clear to the Supermarine design team that the Spitfire's performance at speeds greater than 480 miles per hour (770 km/h) was compromised by the aeroelasticity of its elliptical wing.

Specification No 470 was issued by Supermarine on 30 November, A new wing has been designed for the Spitfire with the following objects: 1) To raise as much as possible the critical speed at which drag increases, due to compressibility, become serious.

[3]Specification 470 described how the wing skins were to be relatively thick, aiding rotational stiffness, which was needed for good aileron control at high speeds.

[7][note 2] The new wing was fitted to a modified Spitfire XIV (serial NN660)—the specification having been amended by the Air Ministry from its original instruction for a Mk VIII fuselage to be used.

[1] NN660 was first flown by Supermarine's chief test pilot Jeffrey Quill from Vickers' flight development site at RAF High Post, Wiltshire, on 30 June 1944.

[8][10] No reason for the loss was established, although the subsequent accident report discussed the possibility that the aileron control rods had momentarily seized or become disconnected during the flight.

Flight testing showed that performance was better than that of the equivalent Spitfire, but not as good as expected, and anything (including splashes of mud or dead insects) on the wing broke the laminar flow and reduced speed.

[12] The Spitfire's fuselage was redesigned to improve the pilot's sightline for deflection shooting and to use a larger fin and rudder to eliminate directional instability.

[9] Subsequent modifications used to try to resolve faults found during trial flights included altering the wing section, and enlarging the fin, rudder, tailplane and elevators.

"[16] The Air Council was told in October 1943 that the British Prime Minister Winston Churchill was "interested in the choice of name" and wanted to discuss it with the Secretary of State.

[16] In November, needing to settle the matter, the Council decided that the Spitfire XXI would be named Valiant, provided the Admiralty agreed.

However, Supermarine objected to Valiant and wanted one starting with the letter S. Portal suggested Spiteful which was accepted without discussion at a meeting in March 1944.

A week later, it sustained damage when Quill had to make a forced landing at RAF Boscombe Down but was repaired and returned to flight.

[19] With the advent of jet propulsion, the order was cancelled in May 1945, a few days before the end of the war in Europe, with only a handful of Spitefuls built.

[20] By March 1946, Supermarine was informed that the RAF only needed the Spiteful as a "low altitude attack aircraft" and during the year RB516 was sent to the Aeroplane & Armament Experimental Establishment to see if the design had value as a fighter-bomber.

The E.10/44 was not ordered by the Royal Air Force (RAF) due to its performance not being much better than the Gloster Meteor and de Havilland Vampire.

The final fully navalised F Mk 32 version differed in that it had folding wingtips, a "sting"-type arrester hook, and two three-blade contra-rotating propellers.