Following the maiden flight of the SR.53 in May 1957, the development of the SR.177 became the main focus of activity at Saunders-Roe. At this point, the project was viewed as having considerable large scale potential, as both the RAF and Royal Navy appeared to be set to be customers for the SR.177. The RAF sought to operate it alongside the incoming English Electric Lightning interceptors while, according to aviation author Derek Wood, the Royal Navy also had considerable interest in the programme. When the development contract had been issued in May 1955, it reflected this dual interest. The Navy's requirements were defined in NA.47 while the RAF's requirements were specified in OR.337, which had been issued by the Ministry of Supply as Operational Requirement F.155. There was optimism that a joint aircraft for the two services could be developed, saving considerable expense, time, and effort.