During the time of the Cold War (1947-1991) between East and West, British military power was to figure heavily into the defense of Western Europe should a Soviet invasion ever occur. This meant that its various service branches required all manner of modern technology to meet the threat of the day - namely that from nuclear-capable Soviet bombers.
Many aircraft designs were drawn up during the period to meet various demands: fleet air defense, day-night fighter, high-speed / high-altitude interceptor and so on. By the time of the mid-1950s, serious thought was being given by British authorities to shore up interception capabilities, particularly at high-altitude. This resulted in design studies and a formal requirement being penciled out by the latter part of the decades.
It was requested that a new, all-modern interceptor be developed that carried radar as well as strictly Air-to-Air Missile (AAM) armament controlled by an all-in-one weapon system. To go along with this, three critical factors came into play for Cold War-era interceptors: rate-of-climb, speed, and altitude. As such, a twin-engine (reheat-capable) design was all but necessary augmented by a limited-burn rocket booster unit. This would provide the aircraft with a quick take-off capability, reaching the desired interception altitude, while then achieving Mach 2 speeds to reach the target area. Once in range of radar, attack would commence with beam-riding missiles. To offset the expected onboard workload (now involving piloting, weapons management, and radar management), a crew of two was a must. In turn, this required a pressurized cockpit as well as ejection seats.
Authorities called for a finalized design no later than January 1962, which placed expediency at the forefront above all else.
de Havilland engineers attempted to meet the requirement through their DH.117 submission. It was, rather optimistically, intended that the aircraft could see its first-flight before the end of 1958 and Initial Operational Capability (IOC) could be reached within the intended 1962 timeframe. Up to four flyable aircraft would be constructed for the prototyping and flight-testing phases followed by production-quality units to take into active service.
While the official requirement called for a maximum speed in the vicinity of Mach 2, engineers saw their sleek aircraft flying in excess of Mach 2.3 and was also marketed with a service ceiling of 60,000 feet. Range would be augmented by the addition of wing tip fuel tanks to bolster the already-onboard fuel stores while under full war load. Due to the high speed involved, titanium would factor into the aircraft's overall construction to go along with lightweight, yet strong, alloys.
The DH.177, as proposed, incorporated tapered, straight-edged wing mainplanes low-mounted at midships along the fuselage sides. The mainplanes, made as slim as possible for limited drag, were given noticeable anhedral (downward angle) and were capped by the wing tip tanks. Each member would also feature a single underwing hardpoint to carry an AAM (at this point the "Blue Jay" series was in focus). The cockpit would seat its two crew in tandem aft of the long and slender nosecone housing the radar unit. The fuselage, also long and slender, tapered to a point under the single vertical tail fin. Along the midway span of the rudder were installed the horizontal tailplanes.
The engines were to be housed in nacelles formed into the lower fuselage sides, aspirated via semi-circular ports near the cockpit walls and exhausted through circular ports ahead of the tail unit. To benefit climb and straightline performance, a Spectre Spe.5 booster rocket of 11,000lb thrust was to be embedded into the ventral line of the fuselage. The engines-of-choice became de Havilland's own Gyron Junior afterning turbojets of 12,000lb thrust. Maximum estimated speed was officially Mach 2.35 at altitude.
As drawn up, the DH.117 had an overall length of 68.9 feet with a wingspan of 38 feet. Gross weight was 55,000lb.
Despite the British need and promising scope of the de Havilland proposal, the DH.117 was not to be. A mock-up was completed by de Havilland but little else was had for the project. It went on to join many other abandoned interceptor forms of the period as requirements changed and technology progressed.