The program had progressed only as far as the construction of a single wooden mockup when it was canceled in 1959, due to a shortage of funds and the Soviets' adoption of ballistic missiles as their primary means of nuclear attack.

[2] The specification was laid down on 6 October 1955, calling for an interceptor that could fly at 60,000 ft (18,000 m) at a speed of Mach 1.7 (1,122 mph (1,806 km/h), with a range of 1,000 miles (1,600 km).

[2] A further consideration was that an integrated fire-control system would be fitted, allowing the interception of a bomber at 60 nmi (110 km) and three targets to be destroyed during a single mission.

[3] 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.

[6] 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.

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 278,000 square miles (720,000 km2) per hour.

[8] From September 1958, substantial engineering and design changes were implemented; however, SAC had lost interest in the escort fighter concept.

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.

[16] The large fuselage and wing had two and five fuel tanks, respectively, giving an estimated combat radius of some 1,100 nautical miles (2,000 km).

[5] 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 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.