However, late in 1953 delays in the F-102B program caused the Air Force to reconsider its procurement policy for all-weather interceptors. At that time, the subsonic Northrop F-89 Scorpion was the backbone of USAF long-range all-weather interceptor squadrons, with the supersonic Convair F-102A Delta Dagger just beginning to undergo flight testing. The F-102A had always been considered by the USAF as only an interim interceptor, filling in the void until the far more advanced F-102B could be made available. However, the F-102A was at that time experiencing teething problems on its own and it appeared that its introduction into service might be appreciably delayed. In addition, the explosion of a hydrogen bomb by the Soviet Union in August of 1953 made it imperative that the Air Force find something other than the F-102A that would help fill in the gap between the subsonic F-89 Scorpion and the Mach-2+ F-102B. The Air Force Council invited the aircraft industry to submit proposals. The work was to be done under the aegis of Weapons System WS-217A.
Northrop submitted an advanced version of the F-89 Scorpion, North American offered an all-weather interceptor version of the F-100 Super Sabre, and McDonnell proposed an adaptation of the F-101 Voodoo. In June of 1954, the Air Force deemed the McDonnell proposal the best of the three submissions.
Before being awarded a contract, McDonnell had been looking into both single- and two-seat configurations for their interceptor and had explored several alternative powerplant installations including General Electric J79s, Pratt & Whitney J57s or J75s, or Wright J67s. In November 1954, a two-seat configuration was finally adopted, and it was decided that the powerplants would be a pair of Wright J67s. The Wright J67 was an license-built version of the British Bristol Olympus turbojet which offered a maximum afterburning thrust of 22,000 pounds. The fire control system was to be the Hughes MG-13 system, an improved version of the E-6 system fitted to the Northrop F-89D Scorpion, and the armament was to consist entirely of Hughes Falcon guided missiles equipped with conventional warheads. No internal cannon armament was to be fitted.
The initial go-ahead decision for the interceptor Voodoo was made on February 25, 1955. It was anticipated that the first flight would take place in mid-1956 and that the initial entry into service would be in early 1958. An initial batch of 28 two-seat interceptors was ordered under a Letter of Intent issued on March 3, 1955. On July 12, an official contract increased the fiscal year 1956 order to a total of 96 aircraft. The aircraft seems to have initially been assigned the designation F-109, but the aircraft was officially designated F-101B in August of 1955. A mockup was inspected in September.
However, the Wright J67 engine soon began to encounter serious developmental difficulties, resulting in a delay in the F-101B program. Both McDonnell and the Air Force agreed to switch to a pair of Pratt & Whitney J57-P-55 turbojets fitted with afterburners which were 24 inches longer than those of the J57-P-13 which powered the single-seat Voodoos. These longer afterburners raised maximum thrust rating from 15,000 pounds to 16,900 pounds.
The F-101B retained the center and rear fuselage sections and the wing and tail surfaces of the F/RF-101A. However, it had a revised forward fuselage housing the MG-13 fire control system with automatic search and track mode, a two-seat tandem cockpit with pilot in front and radar operator in the rear, a retractable flight refuelling probe in front of the pilot's cockpit, and an all-missile armament. The internal fuel capacity was reduced to 2053 gallons to provide more room for electronic equipment and armament. Since the F-101B was heavier than its single-seat predecessor, it employed larger tires with a beefed-up undercarriage. Bulges had to be installed in the lower gear doors and in the undersides of the fuselage in order to accommodate the larger tires. Armament consisted of four Hughes GAR-1 semi-active radar homing or GAR-2 infrared-homing Falcon missiles carried on and launched from a rotary armament door covering the fuselage bay beneath and behind the rear cockpit. Two missiles were attached to recessed slots on each side of the door. After the first pair of missiles were launched, the door was flipped over, exposing the other pair. Some references claim that the F-101B carried six Falcons rather than four, but these seem to be in error.
The first flight of the two-seat Voodoo (designated NF-101B, serial number 56-232) took place on March 27, 1957, nearly a year later than predicted back in early 1955. Unlike the airframes of production F-101B, which were stressed for 7.33g maneuvers, the airframe of the NF-101B was limited to 6.33 g maneuvers.
In the next two years, about 50 F-101Bs were accepted and subjected to extensive tests before being released for operational service. Category I flight tests were carried out at Edwards AFB, and Category II and III tests were carried out at Eglin AFB and at Otis AFB, respectively. These tests were completed on March 15, 1959.
During flight testing, problems were encountered with the radar operator's position in the rear cockpit. It had been badly designed, and little could be done except to make minor changes. The Hughes MG-13 fire control system turned out to be inadequate, being merely a refinement of the E-6 fire control system fitted to the F-89D and could not effectively control the weapons of an interceptor as fast as the F-101B. A proposal to replace the MG-13 with the MA-1 system planned for the F-106 was turned down as being too costly. The only option was to improve the Central Air Data Computer that was the heart of the MG-13 system.
The first F-101Bs were delivered to the 60th Interceptor Squadron at Otis AFB in Massachusetts on January 5, 1959. F-101Bs ended up equipping 18 air defense squadrons (the 2nd, 13th, 15th, 18th, 29th, 49th, 59th, 60th, 62nd, 75th, 83rd, 84th, 87th, 98th, 322nd, 437th, 444th, and 445th Fighter Interceptor Squadrons). F-101Bs also served with the 4570th Test Squadron and the 4756th CCTS (later designated the 2nd Fighter Interceptor Training Squadron), both based at Tyndall AFB in Florida. These units carried out operational suitability tests and training for the Air Defense Command.
Late production F-101Bs (blocks 115 and 120) were completed with modified fire control systems and with provisions for carrying a pair of Douglas MB-1 Genie unguided nuclear-armed rockets on the rotary weapons bay in place of the two Falcon missiles. Starting in 1961, many earlier F-101Bs were upgraded to this standard under *Project Kitty Car*. The MG-13 fire control system was capable of hands-off Genie launches, including the automatic launch of the rocket, turning the aircraft into the escape maneuver, and detonating the nuclear warhead at the appropriate time. Since the Genies were bigger and created more drag, and also because they were more classified, they were normally carried internally until they were ready to be fired. Then the door would rotate and the rocket was fired.
Between 1963 and 1966, many F-101Bs were fitted with an infrared sensor in front of the pilot's cockpit in place of the retractable refuelling probe. Other modifications were made to the control system as part of the Interceptor Improvement Program (also known as Project Bold Journey). Most F-101Bs were fitted between 1964 and 1968 with a modified pitch control system for the automatic pilot in an attempt to address the ""pitch-up"" problem that had plagued the Voodoo throughout its service life. Included in the upgrades was an enhancement of the resistance of F-101B airframes to electromagnetic pulses, and an improved MG-13 fire control system was installed for use against low-flying targets.
Produced alongside the F-101B interceptor was the F-101F operational and conversion trainer. The two-seat trainer version was initially designated TF-101B. The 79 F-101Fs were equipped with dual controls, but carried the same armament as the F-101B and were fully combat-capable. Most of these F-101Fs were retrofitted with infrared sensors and improved fire-control systems as part of Project Bold Journey .
The last of 480 F-101Bs was delivered in March of 1961. Once the teething troubles with its fire control system had been corrected, the F-101B proved to be a quite successful interceptor. However, it was outshone by the faster and more maneuverable Convair F-106A Delta Dart when that interceptor entered service.
Under a program known as Operation Queens Row, a batch of 56 F-101Bs was delivered to the Royal Canadian Air Force (later renamed the Canadian Armed Forces) between July 1961 and May of 1962. In addition, Canada also received ten F-101F two-seat operational trainers. In Canadian service, they were designated CF-101F.
In 1970-71, the 46 surviving CF-101Bs and CF-101Fs from the initial batch delivered to Canada were traded to the USAF for 56 refurbished and modernized F-101B interceptors and ten new F-101F operational trainers under Operation Peace Wings. These ex-USAF Voodoos were from earlier production batches, but had been upgraded with infrared sensors and improved fire control systems as part of Project Bold Journey.
F-101Bs began to leave active duty with the USAF beginning in 1969, many aircraft being passed along to the Air National Guard. The last active duty USAF squadrons to fly the F-101B were the 60th and 62nd FISs which were deactivated in April of 1971. However, a few F-101Bs continued on with training units for another ten years. The last Voodoo in US service (F-101B-105-MC 58-300) was finally retired by the 2nd Fighter Interceptor Training Squadron at Tyndall AFB in Florida on September 21, 1982.
The first F-101Bs were delivered to the Air National Guard in November of 1969, entering service with the 116th Fighter Interceptor Squadron of the Washington ANG and the 132nd FIS of the Maine ANG. They also served with the 179th FIS of the Minnesota ANG, the 136th FIS of the New York ANG, the 137th FIS of the New York ANG, the 192nd FIS of the Nevada ANG, the 178th FIS of the North Dakota ANG, the 123rd FIS of the Oregon ANG, and the 111th FIS of the Texas ANG. The F-101B passed out of ANG service when the last F-101B was retired by the 11lth FIS in 1981. It had operated the F-101B/F briefly as part of the Tactical Air Command after ADC was inactivated on April 1, 1980.
The Colorado State University operated a civil registered F-101B-110-MC (N8234, ex 57-410) in a research program to study severe storms.
Produced alongside the F-101B interceptor was the F-101F operational and conversion trainer. The 79 F-101Fs were equipped with dual controls, but carried the same armament as the F-101B and were fully combat-capable. Most of these F-101Fs were retrofitted with infrared sensors and improved fire-control systems as part of Project *Bold Journey*. The F-101F was externally identical to the F-101B, and the two aircraft could only be distinguished from each other by an examination of their serial numbers.
Dual-control F-101F aircraft were widespread throughout the F-101 interceptor fleet, but a sizeable proportion of them were concentrated in the training units with only a handfull being assigned to each operational F-101B interceptor unit. Reconnaissance Voodoo units were also assigned a few F-101Fs to assist with their conversion training.