The Republic F-105 Thunderchief is an American fighter-bomber that served with the United States Air Force from 1958 to 1984. Capable of Mach 2, it conducted the majority of strike bombing missions during the early years of the Vietnam War. It was originally designed as a single-seat, nuclear-attack aircraft; a two-seat Wild Weasel version was later developed for the specialized suppression of enemy air defenses (SEAD) role against surface-to-air missile sites. The F-105 was commonly known as the "Thud" by its crews. It is the only American aircraft to have been removed from combat due to high loss rates.
As a follow-on to the Mach 1 capable North American F-100 Super Sabre, the F-105 was also armed with missiles and a rotary cannon; however, its design was tailored to high-speed low-altitude penetration carrying a single nuclear weapon internally. First flown in 1955, the Thunderchief entered service in 1958. The single-engine F-105 could deliver a bomb load greater than some American heavy bombers of World War II such as the Boeing B-17 Flying Fortress and Consolidated B-24 Liberator. The F-105 was one of the primary attack aircraft of the Vietnam War, with over 20,000 Thunderchief sorties flown. Out of the 833 produced, 382 aircraft were lost, including 62 operational (non-combat) losses. Although less agile than smaller MiG fighters, USAF F-105s were credited with 27.5 kills.
During the conflict, the single-seat F-105D was the primary aircraft delivering heavy bomb loads against the various military targets. Meanwhile, the two-seat F-105F and F-105G Wild Weasel variants became the first dedicated SEAD platforms, fighting against the Soviet-built S-75 Dvina (NATO reporting name: SA-2 Guideline) surface-to-air missiles. Two Wild Weasel pilots were awarded the Medal of Honor for attacking North Vietnamese surface-to-air missile sites, with one shooting down two MiG-17s the same day. The dangerous missions often required them to be the "first in, last out", suppressing enemy air defenses while strike aircraft accomplished their missions and then left the area.
When the Thunderchief entered service it was the largest single-seat, single-engine combat aircraft in history, weighing approximately . It could exceed the speed of sound at sea level and reach Mach 2 at high altitude. It was conceived of as an internal project to produce a replacement for the RF-84F Thunderflash, which first used the characteristic wing-root air intakes to make room for cameras in the nose section. The design team led by Alexander Kartveli examined some 108 configurations before settling on a large, single-engine AP-63FBX (Advanced Project 63 Fighter Bomber, Experimental), specifically AP-63-31. Traditional fighter attributes such as maneuverability were a secondary consideration.
During April 1952, Republic made its contractor proposal, which contained many of the features that the United States Air Force (USAF) would have liked the RF-84F to have been outfitted with had it been technically possible; one month later, the Air Staff endorsed its development over that of further developing the RF-84F. However, by March 1953, the USAF had reduced the order to 37 fighter-bombers and nine tactical reconnaissance aircraft, citing the approaching end of the Korean War. In October 1953, the F-105 mock-up was inspected; no major changes were recommended.
Initial flights
thumb|Republic YF-105A, AF Ser. No. 54-0098, the first of two prototypes
On 22 October 1955, the YF-105A prototype made its maiden flight. After 22 hours of flight time, the prototype was returned to the factory for repairs after sustaining major damage. Both aircraft featured conventional wing root air intakes and slab-sided fuselages typical of the early jets; Republic viewed the prototypes as not being representative of the true capability of the aircraft due to numerous changes that were enacted prior to production. Specifically, insufficient power and aerodynamic problems with transonic drag, as well as Convair's experience with their F-102, had led to a redesign of the fuselage to conform to the area rule, giving it a characteristic "wasp waist". The F-105's reworked air intake was designed with a unique forward-swept shape, which was derived from Antonio Ferri's work on the proposed Republic XF-103 ramjet-powered interceptor. In combination with the distinctive forward-swept variable-geometry air intakes, which regulated airflow to the engine at supersonic speeds, and the J75 engine, this redesign enabled the F-105B to attain Mach 2.15.
alt=This is a flightline of F-105s of the 17th.|thumb|The 17th Wild Weasel squadron with a F-105 flightline. The F-105 was also used for "Wild Weasel" anti-radar missions carrying AGMs.
During March 1956, the USAF placed a further order for 65 F-105Bs and 17 RF-105Bs. In order to conduct the nuclear mission, an MA-8 fire control system, AN/APG-31 ranging radar, and K-19 gunsight to allow for toss bombing were integrated. On 26 May 1956, the first pre-production YF-105B made its maiden flight. In June 1957, Republic Aviation requested that the F-105 be named Thunderchief, continuing the sequence of the company's Thunder-named aircraft: P-47 Thunderbolt, F-84 Thunderjet, and F-84F Thunderstreak. The USAF made this name official one month later.
Later development
To fulfill the USAF's requirement for an all-weather attack aircraft, Republic proposed the F-105D variant during 1957.
Development of the RF-105 reconnaissance model was restarted during the late 1950s, for a time based on the F-105D, before work on the model was cancelled for the final time on 23 December 1960. Flight testing of the F-105D was somewhat less troubled than the less advanced F-105B, to the point where the D-model was ready for operational service ahead of its predecessor. Category II flight testing in late 1959 identified various key deficiencies on the F-105B, particularly with the MA-8 fire control system and autopilot of this variant. Production of the F-105 was heavily impacted by the decision taken by Secretary of Defense Robert McNamara to equip no more than seven combat wings with the type. During November 1961, production of the type was cut in favor of the USAF adopting the Navy's F-4 Phantom II, and in the longer term, the General Dynamics F-111 Aardvark of the TFX program. While considerations towards reopening production of the F-105 were discussed in 1967, this interest did not ultimately see any such revival.
The final 143 Thunderchiefs built were of the two-seat F-105F trainer variant. Based on the F-105D, this model was 31 inches (79 cm) longer to provide room for the rear cockpit; otherwise, the aircraft had similar flight performance to the preceding F-105D. A total of 833 F-105s were completed before production ended in 1964. The F-105 had been designed for a short nuclear campaign, leading to shortcomings that became evident in a lengthy conventional war, such as a poor hydraulics layout and fuel tanks that were not self-sealing. Subsequent upgrades improved the reliability and weapons capacity of the existing F-105Ds. In response to the surface-to-air missile threat experienced in the skies above Vietnam, dozens of F-105Fs were converted into anti-radar "Wild Weasel" aircraft, culminating with the F-105G.
Design
Overview
thumb|upright|Front view of Republic F-105B with avionics layout
The F-105 was a mid-wing monoplane with a 45° swept wing and tail surfaces. The single engine was fed by two intakes in the wing roots, leaving the nose free for a radome housing the multi-mode radar. Its fuselage provided room for of fuel and an internal bomb bay. The bomb bay measured by by ; it was originally designed to carry a single nuclear weapon but typically held an additional fuel tank. It featured four under-wing and one centerline pylon; the two inner wing and centerline pylons were capable of accepting fuel from drop tanks. Two outer dry stations were wired for missiles or bombs. One M61 Vulcan (initially designated T-171E3) 20 mm 6-barrel Gatling-style cannon was installed in the left side of the nose. A pair of short-range AIM-9 Sidewinder air-to-air missile could be carried on each of the outer wing pylons.
The F-105 was designed primarily for low-level interdiction and its low-altitude speed was its greatest asset when dealing with enemy fighters such as the MiG-17/J-5s and MiG-21. The F-105 managed 27.5 air-to-air victories. Based on combat experience, the F-105D was updated with a better ejection seat, additional armor, improved gun sights, and Electronic Counter Measures (ECM) pods on the wings.
Flight characteristics
thumb|left|F-105D Thunderchiefs refueling from a [[Boeing KC-135 tanker]]
Former North American F-86 Sabre pilot Jerry Noel Hoblit recalled being in awe of the F-105's size after seeing it for the first time; he could not manage to reach the air intake lip even with a running jump. The F-105 had a spacious cockpit with good visibility and layout (particularly after the introduction of "tape" instruments); the advanced electronics were easy to learn and operate. Takeoffs and landings were often performed in the range. The spoilers provided good roll control at all speeds and the distinctive four-petal airbrakes (which also opened slightly when the afterburner was engaged to allow for the larger flow of exhaust gases) were highly effective even at supersonic speeds. Loss of control due to a spin or complications of adverse yaw required deliberate effort from the pilot and spontaneous spin recovery was rapid. The latter two names arose from the F-105's predecessors, the Republic F-84 Thunderjet and F-84F Thunderstreak, nicknamed "Hog" and "Super Hog", respectively. According to F-105 pilots and crews, the "Thud" nickname was inspired by the character "Chief Thunderthud" from the Howdy Doody television series.
thumb|20mm [[M61 Vulcan firing test aboard an F-105D Thunderchief.]]
The aircraft's offensive capabilities were sarcastically referred to as a "Triple Threat"—it could bomb you, strafe you, or fall on you. Positive aspects, such as the F-105's responsive controls, strong performance at high speed and low altitude, and its outfit of electronics won over some pilots. For some, "Thud" was a term of endearment; retroactively the RF-84F Thunderflash became known as "Thud's Mother". F-105 pilot Colonel Jack Broughton said of the nickname: "The Thud has justified herself, and the name that was originally spoken with a sneer has become one of utmost respect through the air fraternity".
Special modifications
Commando Nail
thumb|The [[cockpit of an F-105 Thunderchief]]
The rear cockpits of several two-seat F-105Fs were modified under project Commando Nail with an R-14A radar and a radar scope that offered high resolution. These aircraft were used for all-weather and night low-level strikes against especially dangerous targets by a unit from the 13th Tactical Fighter Squadron (1966–1975) dubbed "Ryan's Raiders" starting in April 1967. Some of these aircraft were later converted to the Wild Weasel III standard.
In an effort to thwart MiG attacks, several F-105Fs were also fitted with Hallicrafters QRC-128 communication jamming system under project Combat Martin. The North Vietnamese interceptor force followed Soviet air-defense doctrine, with pilots under rigid direction of ground controllers over radio links. The QRC-128, nicknamed "Colonel Computer", filled up the rear cockpit of the F-105F. It bounced voice communications over the radio channel back out after a delay, resulting in an obnoxious garble. However, the first time the Combat Martin was used, the US National Security Agency (NSA), in charge of US strategic signals intelligence, ordered the Air Force to cease and desist immediately, since the NSA believed that the intelligence obtained by monitoring the channels outweighed the benefits of jamming them.
Thunderstick II
Experience in Vietnam demonstrated the need for a better visual and blind bombing capability. In March 1968, the Air Force ordered development of an upgraded bombing/navigation system, incorporating a Singer-General Precision inertial navigation system, improvements to the AN/APN-131 navigation radar, and solid-state circuitry for the R-14A radar, which was redesignated R-14K. Furthermore, the digital AN/ARN-92 long-range navigation receiver replaced the problematic AN/ARN-85 receiver. The additional avionics were housed in a long, raised dorsal spine. The modified bombing/navigation system was known as Thunderstick II. F-105s with this system could achieve a bombing circular error of probability (CEP) of from an altitude of . Although the first Thunderstick II aircraft flew in 1969, they were not used in Vietnam. A total of 30 F-105Ds received this modification. They were initially assigned to the 563TFS/23TFW at McConnell AFB. In the summer 1972, they were all transferred to the newly reactivated 457TFS (AFRES) at Carswell AFB. This remained the only unit to fly the Thunderstick II until its retirement in 1981–82.
Wild Weasel
In 1965, the USAF began operating two-seat North American F-100F Super Sabres specially equipped for Suppression of Enemy Air Defenses (SEAD) missions in Vietnam. Nicknamed the Wild Weasel, these aircraft achieved a number of victories against North Vietnamese surface-to-air missile radars. The second crew member was a Navigator trained as an Electronic Warfare Officer (EWO) to decipher sensor information and guide the pilot towards the targets. However, the F-100F was an interim solution, since its limited payload often required multiple aircraft to conduct a successful strike; it also lacked the speed and endurance to effectively protect the F-105.
thumb|upright=1.15|left|F-105F with armament layout in August 1964; including 20 mm (0.79 in) cannon rounds, 2.75 in (70 mm) rockets, Bullpup and Sidewinder missiles, general-purpose bomb, cluster bombs, LAU-3A Launchers, flare and chaff dispensers and drop tanks.
The resulting EF-105F Wild Weasel III