The F-100D (company design numbers NA-223, -224, -235, and -245) was an improved version of the F-100C fighter-bomber. It was also the most widely produced version of the Super Sabre, over 1200 were built.
The F-100D, intended only to fulfill the fighter-bomber role, was not designed for an air superiority mission. The F-100D had the same six under-wing hard points as the F-100C, but the detachable pylons used forced ejection rather than gravity release for dropping their stores. The size of the vertical tailfin and rudder were increased, and the fin trailing edge featured a larger and wider square protrusion which carried an AN/APR-26 rearward radar warning antenna and the fuel jettison pipe. The standard nose-mounted AN/APR-25 receiving set, used for radar signal detecting and homing, was retained.
The F-100D was equipped with a Minneapolis-Honeywell MB-3 automatic pilot. This device provided the capability to allow the pilot to work with both hands on maps reading or weapons arming while the F-100D flew itself to the target. While flying in formation with other aircraft, the autopilot was not used. Improved electronic low altitude bombsite (LABS) was fitted so that a MK-7, MK-38, or MK-43 nuclear bomb could be delivered. Conventional bomb loads including six 750-pound or four 1000-pound bombs were the usual configuration.
The first F-100D (54-2121) flew on January 24, 1956 piloted by Dan Darnell. Deliveries to the USAF began in September of 1956; the first recipient was the 405th Fighter-Bomber Wing at Langley AFB, Virginia. It rapidly replaced the F-100C in most USAF fighter wings. By the end of 1956, 79 F-100Ds were in the Tactical Air Command's operational inventory and 136 F-100Ds were in service at overseas bases in Japan, France, and Morocco.
Several major deficiencies were identified during the early service of the F-100D. Among these were a temperamental electrical system, inconsistencies between the autopilot and the low-altitude bombing system linkage, and unacceptable inaccuracy of the MA-3 fire control system. Despite these problems, large numbers of F-100Ds entered the operational inventory before they could be corrected.
Sidewinder air-to-air infrared homing missiles were introduced on the production line with the 184th F-100D. Air-to-air missile armament had initially been tested on six modified F-100Cs. Although initially designed for air-to-ground operations, the addition of air-to-air missiles made the F-100 an air superiority capable platform. Also introduced with the 184th F-100D was a provision for centerline-mounted fuselage attachment points. These points could carry "special stores"-a euphemistic term for nuclear weapons.
Nuclear weapons could be carried on the left wing intermediate attachment point or on the fuselage centerline attachment points. The nuclear weapons that could be carried included the Mk 7, Mk 28 EX, Mk 28 RE, Mk 43, TX-43, and TX-43 X1. Explosive yields ranged from one kiloton to nearly ten megatons, depending on the weapon. For delivery of these nuclear weapons, the F-100D carried the AN/AJB-1B low-altitude bombing system (LABS). This system was used in conjunction with information provided by the A-4 gyro sight to calculate aiming and release information for "toss-bombing" nuclear weapons. In a typical mission, the F-100D would approach the target at very low altitude at approximately 500 mph. Then, the pilot would elevate the nose of the aircraft by using a 4G pull up. Partway into the "toss" maneuver, the computer would automatically release the bomb. The pilot completed his attack maneuver (similar to an Immelman) and egressed the target area at low altitude and very high speed (using afterburner thrust if needed).
In late 1959, 65 F-100Ds were modified to carry the Martin GAM-83A Bullpup air-to-surface missile. The Bullpup missile was optically guided to its target by the pilot using a radio command joystick to impart guidance commands to the missile while keeping a flare on the missile's tail lined up with the target as seen through his gunsight. The GAM-83A differed from earlier Bullpup versions in that it had an improved radio guidance system that freed the operator from the need to align the target with his sight, permitting guidance from an offset position. Delays in Bullpup deliveries caused the operational debut of the first GAM-83A-equipped F-100D squadron to slip to December of 1960. Unfortunately, this missile was to prove almost useless in Vietnam and was withdrawn from action after only a few sorties. Although a failure, the attempt to use precision guided munitions led to more effective weapons in later years.
By the early 'sixties, the F-100D had been subjected to so many in-service modifications to correct its obvious deficiencies that no two F-100Ds were identical. This made for a maintenance and spare parts nightmare. Beginning in 1962, about 700 F-100Ds and Fs were subjected to a series of modifications known as "Project High Wire," a major standardization and upgrading program. The goal of this program was to extend the variety of non-nuclear weapons that could be carried, to eliminate excess weight, and to standardize the cockpit and rewire it completely. Perhaps the most readily noticeable modification produced by the *High Wire* program was the addition of a spring-steel tail hook underneath the rear fuselage. This hook was never intended for carrier-based operations, but was intended to engage arresting gear at the end of runways to prevent running off the runway during certain emergency landing procedures. Adding one to their production block numbers distinguished aircraft so modified--for example; the F-100D-25-NA became F-100D-26-NA after modification. These modifications were completed in 1965.
The F-100D was widely used in Vietnam. Several F-100 aircraft initially stationed in the Philippines were deployed to Thailand in May of 1962 to try and restrain the Pathet Lao which was busily overrunning most of northwestern Laos. F-100s were stationed in South Vietnam beginning in February of 1964. The first combat strike by the F-100D was flown on June 9, 1964 when eight F-100Ds of the 615th Tactical Fighter Squadron flew strikes against targets in the Plaines des Jarres, Laos. The first recorded combat loss was an F-100D (56-3085), shot down on August 18, 1964 over Laos.
Following the Gulf of Tonkin incident, USAF F-100Ds began to fly missions over North Vietnam. These missions were generally of two types--MiG-CAP patrols to protect strike aircraft from attack by marauding North Vietnamese fighters and fighter-bomber strikes carried out with conventional iron bombs against ground targets. On April 1, 1965, F-100Ds flew MiG combat air patrol for a strike force of F-105s that were hitting the Thanh Hoa Bridge in North Vietnam. However, the F-100D was not considered an effective fighter in air-to-air combat, since it lacked a powerful radar set and could not carry advanced air-to-air weapons.
Throughout the late 1960s and early 1970s, the F-100s were gradually withdrawn from combat in Vietnam and replaced by more capable types such as the F-105 and the F-4. The last F-100Ds left Vietnam in July of 1971.
Following their withdrawal from Vietnam, numerous USAF F-100Ds were turned over to the Air National Guard and by mid-1972, the Guard had received 335 F-100Ds. The last F-100D was withdrawn from ANG service in 1979.
In early 1964, the Air Force Thunderbirds flight demonstration team began replacing their F-100Cs with Republic F-105 Thunderchiefs. A major F-105 flying accident in May of that year caused the USAF to decide to re-equip the Thunderbirds with eight F-100Ds specially modified for demonstration purposes. The USAF Thunderbirds flight demonstration team operated F-100Ds from July of 1964 until November of 1968, when they converted to the F-4E Phantom.
During an air show at Laughlin AFB in Texas on October 21, 1967, Thunderbird pilot Captain Merrill A. McPeak's F-100D (55-3520) disintegrated in midair during a solo demonstration. Fortunately, he was able to eject safely. McPeak went on to become the USAF's Chief of Staff from 19xx-xx. The catastrophic wing failure was caused by a series of cracks that had been produced in the wing spars by metal fatigue. The Thunderbirds were temporarily grounded until their planes could be fixed.
Some losses in Vietnam were also thought to have been caused by this problem rather than by enemy action. Because of this, the entire F-100D fleet was temporarily restricted to a 4-G maneuver limit until all the planes could be repaired. This required a complete modification of the wing structural box. These modifications were not completed until 1969.
A succession of in-service difficulties and problems beset the F-100D throughout its career. The safety record of the F-100D left a lot to be desired. Over five hundred were lost in accidents between mid-1956 and mid-1970, far more than were lost in combat in Vietnam.
F-100D 56-3440 is in storage at the Paul E. Garber Facility of the Smithsonian Institution.