North American's company designation was "NA-257", although it was basically identical to the NA-236. At the time, Air Defense Command anticipated an order for 480 aircraft. The resulting design went through considerable evolution, owing to both its cutting-edge technology and continual redefinition of the USAF requirements. Early revisions prominently featured canards, with a span of , and a wing of 53.5° sweep. The aircraft in this configuration would have had a maximum takeoff weight of with a operational ceiling. In addition to the F-108's interceptor role, North American proposed it as a penetration fighter to aid its own B-70 Valkyrie supersonic bomber prototype. Commonality between the B-70 bomber and the F-108 included the escape capsule and General Electric YJ93 engines. Another role considered was for the F-108 to be "gap-fillers" for the Distant Early Warning (DEW) system; because of its great speed, the F-108 could have scanned up to per hour. From September 1958, substantial engineering and design changes were implemented; however, SAC had lost interest in the escort fighter concept. To accompany the B-70 all the way to its target and back, the F-108 in its initial concept would have, at best, marginal range. On 30 December 1958, YF-108A preproduction aircraft on order were reduced from 31 to 20 test aircraft and the first test flight was delayed from February to April 1961. The eventual design, which was built as a full-sized XF-108 mockup, was displayed to Air Force officials on 17–20 January 1959. The project was given the name "Rapier" on 15 May 1959, following a contest by the Air Defense Command asking airmen for suggestions. Cancellation Even as the XF-108 program was progressing well, there were signs that would ultimately lead to its eventual cancellation. Unconfirmed Soviet bomber threats, the overwhelming trend toward offensive and defensive nuclear missiles in the late 1950s and early 1960s, as well as rising costs, contributed to the termination of the XF-108. The cancellation was announced on 23 September 1959. North American continued refining the design through 1960 in hopes that the program might be revived. Despite the extra money and time spent on the Rapier, it was not wholly in vain; the North American A-5 Vigilante supersonic carrier-based nuclear strike bomber developed for the U.S. Navy, which was later modified into a carrier-based reconnaissance aircraft, retained the fuselage/weapon package and systems design of the Rapier. In many ways the Vigilante could