The Royal Navy envisaged a need for an aircraft that could shadow enemy fleets at night and the resulting Specification S.23/37 called for a slow flying low noise aircraft with a long range, capable of operating from an aircraft carrier’s flight deck.
The specified performance was to be a speed of 38 knots at 1,500 ft (460 m) for not less than six hours.
Five companies showed interest, Percival, Short Brothers, Fairey Aviation, General Aircraft Ltd and Airspeed.
General Aircraft submitted the G.A.L.38, of very similar general design to the AS.39.
General Aircraft and Airspeed were selected to build two prototypes each and Airspeed received a contract on 10 August 1938.
The AS.39 was a high wing, semi cantilever, strut braced (on the outer panels) monoplane with wooden wings and tail unit and an all-metal monocoque fuselage.
It had a fixed, divided type landing gear and tail wheel.
The observation aircraft had a crew of three: pilot, observer and radio operator.
The AS.39 had a unique crew configuration with the observer accommodated in the nose with clear vision windows on three sides and the pilot’s compartment raised to allow passage to the radio operator’s compartment.
Four small 130 hp Pobjoy Niagara V seven cylinder air cooled radial engines were mounted on the wings.
This maximized propwash over the wing giving extra lift at low speed.
The wings could be folded for storage when used on an aircraft carrier.