At the close of World War 2 (1939-1945) in 1945, the primary threat to the West became the Soviet Union and this spurred the global airpowers of the day (the United States, Britain, and France) to concentrate on development of a new generation of warplanes centered around a jet propulsion scheme. Engineers went to work and devised a multitude of solutions, many of which were destined to fall to naught, while others began either instant classic or largely forgettable entries.
Britain's Royal Air Force (RAF) has made good on one aspect of their defense-building - the ncuelar-capable "V-bomber" force centered on the Avro Vulcan, the Handley Page Victor, and the Vickers Valliant. It was soon realized that the service was also in need of a high-performance, high-altitude, supersonic reconnaissance platform to size up enemy strength. This led to a new requirement centered on a radar-equipped, day/night, all-weather, high-speed, high-flying reconnaissance platform through Specification "R.156T".
The new requirement was established in 1954 and, the following year, no fewer than five British aero-concerns took part in supplying varied submissions. Basic requirements were laid out: an operating ceiling as high as 70,000 feet with Mach 2.5 speeds being possible - the aircraft would avoid enemy ground-based defenses and interceptors through high altitude operation and sheer speed. The Air Ministry looked to have the new design settled as soon as 1960.
Avro engineers penciled out a futuristic design built around the prospect of very-high-speeds with the minimum of generated drag. The resulting, finalized design took on a dart-like overall shape in which the front of the fuselage was detailed only by canard foreplanes and an embedded cockpit while the aft-section carried a single vertical tail fin and seated the mainplanes. The mainplanes were given sweepback only along their leading edges and, within each member, would be buried the powerplants. The engines were to be aspirated by cone-capped (two-stage shock) intakes (set ahead of the leading edge) and exhausted aft through conventional ports (aft of the trailing edge). An early design shape of 1955 carried the engines in nacelles at the wingtips but more or less maintained the same sleek design appearance. This approach was, however, abandoned. Wing-mounted engines were also championed from the outset for they supported maintenance access and outright unit replacement - the latter allowing the aircraft to feature any new, or different, propulsion scheme with little change to the overall airframe.
An unconventional four-legged undercarriage would be featured to allow for the needed ground-running - a single nose leg paired with a inline main leg, these supported by outriggers set near each engine nacelle.
The embedded cockpit meant that the pilot was not granted conventional vision from his position. Rather, he would operate the aircraft through a periscope-type arrangement which would have presented issues all its own and require specialized training.
Multiple engine fits were considered for the Model 730, numbering as few as four units and as many as sixteen total turbojets. The operating crew was to be two, three, or four personnel but would have included at least one pilot and one or two navigators. Throughout the development process, the target all-up weight remained 200,000lb of which half would have to be committed to the necessary fuel stores for feeding the thirsty engines.
Between the nose section and main landing gear legs would be housed the side-looking "Red Drover" X-band aerial radar unit - critical to the mission success of the aircraft. The Mach 2.5 requirement ensured that the aircraft would have to incorporate steel (honeycomb sandwich) into its design which proved complex when compared to alloys but necessary to combat heat generation at the speeds and operating altitudes required of the aircraft.
The finalized form of the Model 730, as submitted to Air Ministry authorities, incorporated 4 x Armstrong Siddeley P.159 afterburning turbojet engines of 20,750lb thrust coupled with 2 x Armstrong Siddeley rocket motors offering additional thrust only during take-off actions.
Avro engineers targeted a first-flight before the end of 1959 to which three more flyable examples would join the program the following year. From this work would be had production-quality forms for in-service testing to which formal adoption would have come in 1964 of thereabouts. However, cancellation of the project came in 1957 (by way of the infamous "Defence White Paper") when the first prototype was still under construction. It was perceived that advancements in Soviet air defenses would have negated any performance benefits of the Model 730 by the time it would have entered service. Additionally, British through turned towards a future battlefield owned by missiles.
Beyond a completed mockup, partial prototype, and some early wind tunnel testing completed, there was little to be shown for the funding, work, and time put into bringing the complex Avro 730 to fruition.
The Americans found greater success in development of their own high-altitude supersonic reconnaissance platform at about the same time, this becoming the Lockheed SR-71 "Blackbird" spyplane detailed elsewhere on this site.