The development of the Argosy can be traced back to the development of Operational Requirement 323 (OR323) by the British Air Ministry. During 1955, a specification was issued based upon OR323, which sought a medium-range freight aircraft that would be capable of lifting a maximum payload of 25,000 lb (11,340 kg), while also possessing a range of when carrying up to . British aviation manufacturer Armstrong Whitworth Aircraft took interest in this specification and decided to allocate members of its design team to the task of developing a suitable aircraft to meet its demands. Initially, design efforts were focused upon a twin-engine design intended for military use, which was internally designated as the "AW.66".