The "transonic" flight envelope in the field of aeronautics exists between Mach 0.72 up to the speed of sound at Mach 1.0 assuming ideal conditions. This potential lethal "sweet spot" was encountered by airmen of World War 2 (1939-1945) but research was limited with the prop-driven aircraft available during the period. It was not until the advent of viable turbojets that the field could be pushed further along and, in the immediate post-war world and throughout the 1950s, great strides were made by global powers to reach the once-unreachable "breaking of the sound barrier".
For Britain, the road to supersonic flight was ultimately had through a myriad of sleek and powerful designs - some materializing and others remaining merely concepts. In the latter, the concern of Armstrong Whitworth drew up plans for their "AW.58", a swept-wing, single-seat / single-engine research airplane intended to solve some of the riddles of transonic flying - and potentially lead the way to a fully-fledged cannon-armed, radar-equipped military fighter form based on its design. The aircraft was detailed in a proposal during November 1948.
The aircraft drew upon what was then known to be the required qualities of a high-performance platform - namely a turbojet engine, efficient streamlining, and swept-back wing surfaces. The resulting design incorporated all of these traits: the cockpit was buried in the forward section of the fuselage with adequate vision for the sole pilot, the mainplanes (swept back some 60 degrees) were seated at midships and mid-mounted along the fuselage sides while exhibiting considerable sweepback, and the turbojet engine was buried within the aft-section of the tubular fuselage. The nose of the aircraft was cut-off to act as an intake (oval in its general shape) and aspirate the air-breathing engine within. The tail unit was of a "T-style" arrangement featuring a single, swept-back vertical fin and a pair of high-mounted, all-moving swept-back horizontal planes. A retractable tricycle undercarriage was planned for ground-running (single nose leg with two main legs near center mass).
The engine of choice centered on the Rolls-Royce "Avon" series, original designated the "AJ.65". This single unit could output 6,500lb of thrust and was to be exhausted through a circular ring found just under the tail unit (the tail unit extended just over the exhaust port). Estimated performance encompassing the engine and sleek design form included a maximum speed of Mach 1.07.
Dimensions included a running length of 45.1 feet with a wingspan of 24 feet. Gross weight was estimated at 12,000lb. A production fighter would have featured slightly larger dimensions to accommodate additional equipment, fuel, and weaponry.
As a research-minded aircraft, the AW.58 was not intended to carry armament of any kind though a realized military model, that would have been spawned from the AW.58 work would most likely have been equipped with 2 x 30mm automatic cannons near the nose.
The AW.58 existed only as a design study and was not accepted by authorities for further work - thus never progressing beyond its paper stage.