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Operational Requirement F.155 was a specification issued by the British Ministry of Supply for an interceptor aircraft to defend the United Kingdom from high-flying supersonic bombers. Although a nuclear threat from Soviet nuclear-armed bombers was identified as early as in 1955, F.155 calling for supersonic interceptors (which would ideally be in service by 1962) was superseded by the 1957 Defence White Paper, a major review of military spending. One of its key elements was the cancellation of nearly all manned fighter projects, as a radical change had occurred in strategic threats with the expectation that intercontinental ballistic missiles and low-level strikes would replace high flying bombers.

Operation Requirement F.155 specified exacting demands; this machine was to be capable of all-weather interception of targets within 20 minutes of target contact (250 miles from the UK), flying at 60,000 feet and Mach 1.3, using guided weapons (a mixture of infra-red guided missiles and radar guided missiles). From start up, the fighter was to reach 60,000 feet at a range of 70 nautical miles from base in 6 minutes, at a speed of at least Mach 2. A crew of two was also specified because of the anticipated workload. This specification went out to several aircraft companies, and several British aircraft manufacturers submitted their designs for planes that would meet the RAF's specified requirements.

Among these were Armstrong-Whitworth's AW.169:

De Havilland's DH.117:

English Electric's P.8:

Fairey's Delta III:

Hawker's P.1103:

Saunders-Roe's P.187:

and Vickers-Armstrong's Type 559:


Due to the length of design and development, for the interim the RAF also considered purchasing the Canadian Avro Arrow, projected to be operational by 1961, to meet this specification:


So then, what if the 1957 Defence White Paper hadn't terminated nearly all British manned fighter development projects, and one of these aircraft had been ordered to meet Operational Requirement F.155? Which one would have been the most interesting?
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