Editing Avro Vulcan (section)

===Origins===
{{further|V bombers}}
[[File:Avro 698 and Avro 710 top-view silhouettes.png|thumb|Silhouettes of an early Avro 698 concept and the cancelled [[#Avro_707_and_Avro_710|Avro 710]]]]
The origin of the Vulcan and the other V bombers is linked with early [[Blue Danube (nuclear weapon)|British atomic weapon programme]] and [[Deterrence theory#Nuclear weapons and deterrence|nuclear deterrent]] policies. Britain's atom bomb programme began with Air Staff Operational Requirement OR.1001 issued in August 1946. This anticipated a government decision in January 1947 to authorise research and development work on atomic weapons, the U.S. [[Atomic Energy Act of 1946]] (McMahon Act) having prohibited exporting atomic knowledge, even to countries that had collaborated on the [[Manhattan Project]].<ref>Wynn 1997, pp. 7, 16.</ref> OR.1001 envisaged a weapon not to exceed {{convert|24|ft|2|in|m|abbr=on}} in length, {{convert|5|ft|m|abbr=on}} in diameter and {{convert|10000|lb|kg|abbr=on}} in weight. The weapon had to be suitable for release from {{convert|20000|to|50000|ft|m|abbr=on}}.<ref>Wynn 1997, p. 18.</ref>

In January 1947, the [[Ministry of Supply]] distributed [[List of Air Ministry specifications|Specification B.35/46]] to UK aviation companies to satisfy Air Staff Operational Requirement OR.229 for "a medium range bomber landplane capable of carrying one {{convert|10000|lb|kg|abbr=on}} bomb to a target {{convert|1500|nmi|mi km}} from a base which may be anywhere in the world." A cruising speed of {{convert|500|kn|mph km/h}} at altitudes between {{convert|35000|and|50000|ft|m|abbr=on}} was specified. The maximum weight when fully loaded should not exceed {{convert|100000|lb|kg|abbr=on}}. Alternatively, the aircraft was to be capable of carrying a conventional bomb load of {{convert|20000|lb|kg|abbr=on}}. The similar OR.230 required a "long-range bomber" with a {{convert|2000|nmi|mi km}} radius of action with a maximum weight of {{convert|200000|lb|kg|abbr=on}} when fully loaded; this requirement was considered too exacting.<ref>Wynn 1997, pp. 44–46.</ref> Six companies submitted technical brochures to this specification, including Avro.<ref>Wynn 1997, p. 47.</ref>

Required to tender by the end of April 1947, work began on receipt of Specification B.35/46 at Avro, led by technical director [[Roy Chadwick]] and chief designer [[Stuart Davies (engineer)|Stuart Davies]]; the type designation was ''Avro 698''. As was obvious to the design team, conventional aircraft could not satisfy the specification. No worthwhile information about high-speed flight was available from the [[Royal Aircraft Establishment]] (RAE) or the US.<ref>The Vulcan Story by the Technical Editor, Flight, 31 January 1958, p.143</ref> Avro were aware that [[Alexander Lippisch]] had designed a delta-wing fighter and considered the same delta configuration would be suitable for their bomber.<ref>The Avro Type 698 Vulcan The Secrets Behind Its Design And Development, David W. Fildes 2012, {{ISBN|978 1 84884 284 7}}, Bob Lindley recollections p.18</ref> The team estimated that an otherwise conventional aircraft, with a swept wing of 45°, would have doubled the weight requirement. Realising that swept wings increase longitudinal stability, the team deleted the tail ([[empennage]]) and the supporting [[fuselage]], it thus became a swept-back [[flying wing]] with only a rudimentary forward fuselage and a fin ([[vertical stabilizer]]) at each wingtip. The estimated weight was now only 50% over the requirement; a delta shape resulted from reducing the [[wingspan]] and maintaining the wing area by filling in the space between the wingtips, which enabled the specification to be met.<ref name='gunst143'>Gunston, W.T. [http://www.flightglobal.com/pdfarchive/view/1958/1958%20-%200139.html?tracked=1 "The Vulcan Story."] ''Flight'', 31 January 1958, p. 143.</ref> Although Alexander Lippisch is generally credited as the pioneer of the delta wing, Chadwick's team had followed its own logical design process.<ref name='laming23-24'>Laming 2002, pp. 23, 24.</ref> The initial design submission had four large turbojets stacked in pairs buried in the wings on either side of the centreline. Outboard of the engines were two [[bomb bay]]s.<ref name='gunst143'/>

In August 1947, Chadwick was killed in the crash of the [[Avro Tudor|Avro Tudor 2 prototype]], and was succeeded by Sir William Farren.<ref name='laming26'>Laming 2002, p. 26.</ref> Reductions in wing thickness made incorporating the split bomb bays and stacked engines impossible, thus the engines were placed side by side in pairs on either side of a single bomb bay, with the fuselage growing somewhat. The wingtip fins gave way to a single fin on the aircraft's centreline.<ref name='gunst143'/> Rival manufacturer Handley Page received a prototype contract for its crescent-winged [[Handley-Page Victor|HP.80]] B.35/46 tender in November 1947.<ref name='laming26'/> Although considered the best option, the contract award for Avro's design was delayed while its technical strength was established.<ref name ='but 31'>Buttler 2003, p. 31.</ref> Instructions to proceed with the construction of two Avro 698 prototypes were received in January 1948.<ref name='laming26'/> As an insurance measure against both radical designs failing, [[Short Brothers]] received a contract for the prototype [[Short Sperrin|SA.4]] to the less-stringent Specification B.14/46. The SA.4, later named Sperrin, was not required. In April 1948, [[Vickers-Armstrongs|Vickers]] also received authority to proceed with their [[Vickers Valiant|Type 660]], which, although falling short of the B.35/46 Specification, but being of a more conventional design, would be available sooner. This plane entered service as the Valiant.<ref>Wynn 1997, pp. 52–54.</ref>