Operational Requirement F.155 was a specification issued by the British Ministry of Supply on 15 January 1955 for an interceptor aircraft to defend the United Kingdom from Soviet high-flying nuclear-armed supersonic bombers.
Discussion about the need for a new supersonic interceptor had been ongoing for some time in the early 1950s, and several designs introduced, but improving radar systems and weapons mooted the need for better aircraft in the short term. Information about new Soviet supersonic bomber designs emerged in 1954, sparking serious consideration for the first time. The Requirement emerged as a much larger and longer-range system than previously studied. The Requirement called for aircraft to be in service by 1962, the same date as the Tupolev Tu-22.[a]
A number of designs were entered into the competition, many of them based on earlier projects. They generally featured two engines, mounted a powerful new aircraft interception (AI) radar, and would be armed with improved versions of the de Havilland Firestreak missile or an even larger radar-guided design known as "Red Hebe". In overall terms, the F.155 designs were similar to the Convair F-106 or Avro Arrow, although longer range was desired.
Serious design work had only just started when the entire effort was cancelled as part of the 1957 Defence White Paper. This paper considered the introduction of new Soviet medium range ballistic missiles (MRBMs) that were being deployed in East Germany; these were armed with chemical warheads, but it was clear that nuclear-armed versions would be available by the mid-1960s. In this case, shooting down bombers would have no ultimate effect on the outcome of the battle. The paper led to the cancellation of nearly all crewed fighter projects as well as most other air defence programs as a radical change had occurred in strategic threats with the expectation that missiles and low-level strike would replace high-flying bombers.
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