North American XF - 108 Rapier The North American XF - 108 Rapier was a proposed long - range , high - speed interceptor aircraft designed by North American Aviation intended to defend the United States from supersonic Soviet bomber s . To limit development costs , the program shared engine development with the North American XB - 70 Valkyrie strategic bomber program , and used a number of elements of earlier interceptor projects . The program had progressed only as far as the construction of a single wooden mock - up when it was cancelled in 1959 , due to a shortage of funds and the Soviet ' s adoption of ballistic missile s as their primary means of nuclear attack . Had it flown , the F - 108 would have been the heaviest fighter of its era . Following the program ' s termination , the fire - control system , incorporating the Hughes GAR - 9 missile , was adapted for the Lockheed YF - 12 , which was itself canceled . Development . During the early 1950s , the USAF proposed a very high - performance , long - range interceptor . On 20 July 1955 , formal development of what became known as the Long - Range Interceptor , Experimental ( LRI - X ) was approved , planned as a F - 102 Delta Dagger / F - 106 Delta Dart replacement . The specification was laid down on 6 October 1955 , calling for an interceptor that could fly at at a speed of Mach 1 . 7 ( , with a range of . It was to have a two - man crew and at least two engines . A further consideration was that an integrated fire - control system would be fitted , allowing interception of a bomber at and three targets to be destroyed during a single mission . Of the eight interested companies , contracts for preliminary studies were issued to North American Aviation , Lockheed and Northrop on 11 October 1955 , five days after the specification ' s release . Of the paper designs , the North American proposal , dubbed " NA - 236 " , seemed the most promising . The NA - 236 shared some similarities with the XF - 108 , although the most obvious differences were the additions of two finlets at the midspan of the horizontal stabilizers , and canards . Political and budgetary difficulties led to the cancellation of the program on 9 May 1956 . After considerable confusion , the program was reinstated on 11 April 1957 with North American awarded a contract for two prototypes . The designation F - 108 was issued , also known as " Weapon System 202A " . 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 19 ft 10 in ( 6 . 04 m ) , and a wing of 53 . 5° sweep . The aircraft in this configuration would have a maximum take - off weight of 99 , 400 lb ( 45 , 088 kg ) with a 72 , 550 feet ( 22 , 113 m ) operational ceiling . In addition to the F - 108 ' s interceptor role , North American proposed it as an escort fighter for 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 pre - production 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 mock - up , 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 which 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 . 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 reconnaissance bomber developed for the U . S . Navy retained the fuselage / weapon package and systems design of the Rapier . In many ways the Vigilante could be seen as the successful application of the Rapier design principles in a Mach - 2 supersonic design . Hughes Aircraft would continue development of the advanced fire control system and the GAR - 9 missile . Development of the F - 108 radar and missiles was continued by the USAF and the system was eventually used in the Lockheed YF - 12 program . The final configuration for the rear cockpit in the YF - 12A looked similar to that of the F - 108 since it incorporated the same displays and controls required for the Hughes ASG - 18 fire control system . Design . The initial F - 108 configuration featured a very large " cranked " delta wing . There were fixed ventral stabilizers on the wings , mounted at mid - span , and a tall all - moving vertical tailfin , supplemented by two ventral stabilizers that extended when the landing gear retracted . Although some earlier versions of the design had had separate tailplanes and later forward canards , both were abandoned in the final design . The large fuselage and wing have two and five fuel tanks , respectively , giving an estimated combat radius of some . Top speed was estimated at , about Mach 3 , at . The aircraft was powered by two General Electric J93 turbojet engines , also used in North American ' s XB - 70 Valkyrie bomber , in the fuselage . The F - 108 was intended to carry the Hughes AN / ASG - 18 radar , the U . S . ' s first pulse - Doppler radar set . It was to have look - down / shoot - down capability , but could only track one target at a time . The radar was paired with an infra - red search and tracking ( IRST ) system on the wing leading edges . The radar was used to guide the Hughes GAR - 9 ( later redesignated AIM - 47 ) air - to - air missile , three of which would be carried on a rotary launcher in an internal weapons bay . The GAR - 9 was a very large , long - range weapon with its own radar set for terminal homing . It was intended to fly at Mach 6 , with a range of almost .