Development of the Argosy originates in the "AW.66", a proposed twin-engined military transport that was designed with British Air Ministry's Operational Requirement 323 (OR323) in mind. While Armstrong Whitworth terminated work on the AW.66, it decided to go forward with a civilian-oriented derivative of the design, designated "AW.65", as it was judged to be commercially viable. The AW.65 was redesigned to use four Rolls-Royce Dart turboprop engines, and thus was re-designated as the "AW.650". On 8 January 1959, the first Argosy conducted the type's maiden flight. On December 1960, the type received Federal Aviation Administration (FAA) type certification, enabling the initial civil version, referred to as the "Series 100", to enter civil service across most parts of the world.