The Argosy came from the Air Ministry “Operational Requirement 323” (OR323) which resulted in a specification issued in 1955 for a medium-range freight aircraft capable of lifting 25,000 lb (11,340 kg) and that had a range of 2,000 mi (3,200 km) with 10,000 lb (4,500 kg). This led AW to develop a twin-engine design for the military, the AW.66. The potential for civil sales led to a civil design AW.65, which differed by having full section doors at each end of the fuselage to allow quick loading and unloading. A lack of funds led to abandonment of the military requirement, but Armstrong Whitworth had already decided to go ahead with the civil variant as a private venture, it being redesigned with four Rolls-Royce Darts as the AW.650.
The AW.650 was a high-wing four-engined general-purpose transport aircraft, powered by four Rolls-Royce Dart turboprop engines driving Rotol four-blade propellers. The tailplane was on twin booms from the inner engine nacelles, leaving the cargo doors at the rear of the fuselage clear for straight-in loading, while sideways-opening doors were fitted at both ends of the fuselage, with the flight deck high up in the nose. This gave an unobstructed cargo space measuring 10 by 47 feet (3.0 m × 14 m) with a sill height corresponding to that of a normal flatbed truck. This unusual “pod and boom” structure would earn it the nickname “The Whistling Wheelbarrow”. It had a maximum weight of 88,000 lb (39,915 kg) and a payload of 28,000 lb (12,700 kg). Cruising at 276 mph (444 km/h), it had a range of 1,780 mi (2,865 km) and could seat 89 passengers. The first Argosy made its maiden flight on 8 January 1959, receiving Federal Aviation Administration type certification on 2 December 1960. 10 of the initial civil version, the Series 100, were built.
While the RAF had lost interest in the original AW.66, it still needed to replace its obsolete piston engineed Vickers Valettas and Handley Page Hastings, and in 1959 the British Air Ministry drew up a specification for a military derivative of the AW.650 to serve as a medium-range transport, paratroop and supply aircraft. The resultant design, the AW.660, was significantly different from the AW.650. It had the nose door sealed to take a weather radar radome, the rear doors were changed to ‘clam shell’ style with an integral loading ramp, a stronger cargo floor was fitted. Two doors were fitted, one each on the starboard and port sides, to enable paratroopers to exit. The military Argosy had four Rolls-Royce Dart 101 turboprops and had twice the range of the civil Series 100. The new clamshell doors were tested on the second Argosy Series 100 from July 1960, while the first of the RAFs 56 Argosies flew on 4 March 1961.
British European Airways was interested in the Argosy as a replacement for its piston engined freighters, but the payload capacity of the Series 100 meant that it would not be profitable. In order to save money, the wing had been based on that of the Avro Shackleton, built by another part of the Hawker Siddeley Group, but to meet BEAs requirements, a new wing was designed, of the same aerodynamic design, but with a more modern “Fail safe” structure rather than the Safe-life design of the earlier wing. This produced a wing that was both stronger and lighter, while the new wing did not have a limited fatigue life. The revised version, the Series 200, also had larger cargo doors, integral wing fuel tanks and a modified landing gear.
The first Series 200 flew on 11 March 1964, being followed by six more Series 220s, with more powerful engines. One of these Series 220 aircraft is the sole survivor of its type, being displayed in its final Safe Air colours at Woodbourne, New Zealand. All other 220 Series civil Argosies have either crashed or been scrapped. An eighth Series 220 was not completed and was scrapped.