F-105 Thunderchief

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The Republic F-105 Thunderchief, commonly known as the "Thud" by its crews, was a single-seat supersonic fighter-bomber used by the United States Air Force. The largest single-engined fighter employed by the service, it saw extensive use during the Vietnam War in both strike and SEAD roles.

1 Development
2 Operational history
3 Variants
4 Specifications (F-105D)
5 Operators
6 References
7 External links
8 Related content

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Development

The F-105 began development as a Republic Aviation-funded design intended to replace the F-84F Thunderflash. Team led by Alexander Kartveli examined some 108 configurations before settling on a large single-engine AP-63FBX (Advanced Project 63 Fighter Bomber, Experimental). The new aircraft was intended primarily to penetrate into the Soviet Union at supersonic speeds on a hi-lo-hi mission and deliver a single internally carried nuclear weapon. Thus, the emphasis was placed on low-altitude speed and flight characteristics, range, and payload. Fighter attributes such as maneuverability were a secondary consideration <ref name="Green">Template:Cite book</ref>. Enthusiastic at first, the United States Air Force awarded Republic with a contract 199 aircraft in September 1952. However, by March 1953 the USAF had reduced the order to 37 fighter-bombers and 9 tactical reconnaissance aircraft, citing the approaching end of the Korean War. By the time the F-105 mockup had been completed in October 1953, the aircraft had grown so large that the Allison J71 turbojet intended for it was abandoned in favor of an even more powerful Pratt & Whitney J75. Anticipating protracted development of the engine, it was expected that the first aircraft would use the smaller Pratt & Whitney J57. On 28 June 1954, the USAF officially ordered 15 F-105As under the Weapon System designation WS-306.

The first flight of the YF-105A prototype was made on 22 October 1955, with the second YF-105A following on 28 January 1956. In spite of being powered by a far less potent J57-P-25 engine with 15,000 lbf (66.7 kN) of afterburning thrust (the J75 was expected to make 24,500 lbf (109.0 kN) with afterburner), the first prototype attained Mach 1.2 on its maiden flight. Both prototypes featured conventional wing root air intakes and slab-sided fuselages typical of the early jets. However, aerodynamic problems with transonic drag and insufficient power, as well as Convair's experience with their F-102 Delta Dagger, led to a redesign of the fuselage to conform to the Area rule, giving it a characteristic "wasp waist." In combination with the distinctive forward-swept variable-geometry air intakes and the J75 engine, this enabled the resulting F-105B to attain Mach 2.15.

In March 1956, the USAF replaced its F-105A order with that for 65 F-105B. The first pre-production YF-105B flew on 26 May 1956, and on June 19 the aircraft was officially named Thunderchief, continuing the Republic Aviation's sequence of P-47 Thunderbolt, F-84 Thunderjet, and F-84F Thunderstreak. The first production F-105B flew on 14 May 1957.

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 for the multi-mode radar. At the time the F-105 was the largest single-seat combat aircraft ever built. Its capacious fuselage provided room for 1,160 US gallons (4,460 liters) of fuel and a bomb bay measuring 15 feet 10 inches by 32 inches by 32 inches (4.82 m x 0.81 m x 0.81 m), originally intended for a single nuclear weapon but typically containing an additional 390 US gallon (1,500 liters) fuel tank. Two underwing and one fuselage wet-stores-capable pylons were provided for 450 and 650 US gallon (1,730 liters and 2,500 liters) expendable fuel tanks. Two outboard (dry) stations were wired for missiles or bombs. A single T-171E3 20 mm rotary cannon was installed in the port side of the nose with a magazine for 1,028 rounds of ammunition.

On 11 December 1959, F-105B set a world record of 1,216.48 mph (1,958.53 km/h) over a 100 km (62 mi) circuit.

A total of 833 F-105s were produced before production ended in 1964.

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Operational history

The F-105B entered USAF service with the Tactical Air Command's 335th Tactical Fighter Squadron on 27 May 1958. Typical of advanced aircraft, early F-105 service life was plagued by problems with avionics and the MA-8 fire-control system, with the aircraft requiring some 150 hours of maintenance for each hour of flying time. Most of the problems were addressed under Project Optimize. The lack of spares resulted in the entire F-105B fleet being briefly grounded in 1960. Nevertheless, the Thunderchief became the first aircraft in USAF history to complete its first operational year without a single major accident <ref name="Baugher">Template:Cite web</ref>.

By 1964, the F-105B was relegated to Air National Guard squadrons. It was replaced in frontline service by the definitive F-105D whose advanced NASARR R-14A radar and AN/ASG-19 Thunderstick fire-control system gave it all-weather performance. The R-14A radar also added a terrain guidance capability. The F-105D entered service with 335th TFS in 1960. Designed for a European conflict with the Soviet Union, the F-105D saw considerable deployment in West Germany to provide NATO with tactical nuclear strike capability, and in Japan. Like the F-105B, the -D's early career was plagued with maintenance problems and in-flight failures. The origins of the nickname Thud were far from complimentary – it stood for the sound of an F-105 crashing into the ground. The entire F-105D fleet was grounded in December 1961 and then again in June 1962. Many of the issues were worked out during the production run and early F-105Ds were upgraded with these fixes under project Look Alike by 1964, although engine failures and fuel system problems persisted until 1967.

Meanwhile, the USAF was gradually changing the anticipated F-105 mission from nuclear interdiction to conventional bombing. The Look Alike upgrades increased the aircraft's capacity from four to sixteen conventional 750 pound (340 kg) bombs on underwing and fuselage centerline hardpoints and added the equipment to launch AGM-12 Bullpup air-to-ground missiles. In June 1961 an F-105D delivered 7 tons (15,430 lb) of conventional bombs during a USAF test – at the time a record for a single-engine airplane and a heavier payload than World War II's four-engined heavy bombers such as the B-17 Flying Fortress and the B-24 Liberator. In fact, one of the F-105Ds was named Memphis Belle II after the famed WWII B-17.

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Vietnam War

Image:F-105D.jpg Image:Thud Ridge.jpg In spite of a troubled early service life, the F-105 became a dominant player during the Vietnam War. In a foreshadowing of its Wild Weasel role, the first F-105D combat mission of the war involved an attack of an anti-aircraft artillery site on Plaine des Jarres. The first Thunderchief of the war was also lost in this mission, the pilot safely ejecting. The first strike mission took place on 13 January 1965 with the destruction of the Ben Ken bridge in Laos. Following the start of Operation Rolling Thunder on 1 March 1965, a large number of F-105Ds were deployed in Royal Thai Air Force Bases at Khorat and Takhli. On 2 August 1967, F-105Ds from 335th and 338th TFS made the first of many successful raids on the Paul Doumer bridge.

On a typical combat mission into North Vietnam the F-105D carried two 450 US gallon wing-mounted fuel tanks, a 390 US gallon fuel tank in the bomb bay, and five 1,000 pound (454 kg) or six 750 pound (340 kg) bombs, and required inflight refueling both going to and sometime returning from Hanoi 700 miles (1,125 km) distant. Thunderchiefs would cross the Thud Ridge, Template:Coor dms – a mountain ridge in the Red River valley north of Hanoi – and approach their targets from the northwest at high speed and low altitude. The loop around Hanoi was necessary to avoid some of the world's most heavily defended airspace around the city. The ridge could be used to provide concealment from North Vietnamese radars and SAMs but it was also dotted with anti-aircraft artillery and had a MiG fighter field at the south end. The name Thud Ridge originated from its prominent role in the F-105 missions.

Air combat was a different matter. The F-105 was designed primarily for low-level interdiction and its unequalled low altitude speed was its greatest asset when dealing with small and agile Soviet Mikoyan-Gurevich MiG-17 and Mikoyan-Gurevich MiG-21 fighters. The Thunderchief's highly loaded wing was excellent for speed and smooth ride but not for sustained turns in a dogfight. Nevertheless, the F-105 managed 27.5 air-to-air victories against North Vietnamese aircraft at the cost of 17 aircraft lost to enemy fighters (North Vietnamese pilots claimed to have shot down an additional 23 F-105s but only 17 have been confirmed by USAF <ref name="Baugher" />).

On the basis of combat experience, the F-105D was updated with a better ejection seat, radar homing and warning (RHAW) antenna on the tail fin, additional armor, and protection to the hydraulic system which proved to be very vulnerable to combat damage. The hot and humid climate of Southeast Asia created problems for the capricious electronics, a problem encountered by virtually all advanced US aircraft of the war. High ambient temperatures also exacerbated the F-105's propensity for engine fires due to inadequate cooling of the afterburner. Most of the Vietnam aircraft were eventually fitted with ram-air scoops to ameliorate this.

Unfortunately, the low-altitude attacks and dive bombing brought the F-105s into the range of North Vietnamese anti-aircraft fire and the loss rates were so high that the USAF began experiencing shortages of combat-ready aircraft. As the result, after flying over 20,000 combat missions the F-105 was withdrawn from the theater by November 1970, with the F-4 Phantom II taking its place. A total of 397 aircraft were lost in Southeast Asia, 334 of those in combat. The vast majority of losses were the result of enemy ground fire.

Several two-seat F-105Fs were modified under project Commando Nail with high-resolution R-14A radar and fitted with a high-resolution radar scope in the rear cockpit. These aircraft were used for all-weather low-level strikes against especially dangerous targets by the elite Ryan's Raiders from the 44th Tactical Fighter Squadron starting in April 1967. Commando Nail aircraft were also used to develop tactics for B-58 Hustler bombers in Vietnam, although the Hustler never actually made it to Southeast Asia. Some of the these aircraft were later converted to the Wild Weasel III standard.

In an effort to thwart MiG attacks, several F-105s were also fitted with Hallicrafters QRC-128 VHF jammers under project Combat Martin. With only rudimentary onboard radars, North Vietnamese (Soviet) fighters required ground control direction to locate USAF flights and disruption of communications left the pilots virtually blind. Some of these aircraft were eventually brought to the Wild Weasel III standard.

Persistent problems with the AN/ARN-85 LORAN system resulted in 30 F-105Ds being upgraded to the AN/ARN-92 in a long dorsal spine. Known as Thunderstick II aircraft, these F-105s could achieve a circular error probable of 50 feet (15 m) from an altitude of 15,000 feet (4,570 m). Although the first of these aircraft flew in 1969, they were never deployed to Vietnam.

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Wild Weasel

In 1965, the USAF began operating two-seat F-100F Super Sabres specially equipped for Suppression of Enemy Air Defenses mission in Vietnam. Nicknamed the Wild Weasel, these aircraft achieved 9 confirmed victories against North Vietnamese surface-to-air missile radars. The second crew member was an Electronic Warfare Officer, nicknamed the Bear, whose job was to decipher the information from the aircraft's sensors and guide the pilot towards the targets. However, the F-100F was an interim solution and because of its limited payload it had to rely on accompanying strike aircraft to actually attack the SAM sites. It also lacked the speed and the endurance to effectively protect the USAF's primary strike fighter – the F-105. With twice the payload capacity of the Super Sabre and considerably better performance, the two-seat F-105F was an ideal candidate for a more definitive SEAD platform.

The resulting EF-105 Wild Weasel III supplemented its sensors and electronic jamming equipment with AGM-45 Shrike anti-radiation missiles and conventional bombs, giving it an offensive capability lacking in the F-100F. The first of these aircraft flew on 15 January 1966 and they began arriving in Southeast Asia in June. In a typical mission, a single EF-105F would accompany one or two flights of F-105Ds to provide protection from enemy ground fire. While this strategy was effective in reducing F-105D losses, the Weasel aircraft suffered heavy casualties with five lost by August 1965.

The EF-105Fs were upgraded to the definitive Wild Weasel Thunderchief, the F-105G, with the first aircraft arriving in Southeast Asia in late 1967. It incorporated a considerable amount of new SEAD-specific avionics, including an upgraded RHAW system which required a redesign of the wingtips. To free outboard hardpoints for additional weapons, the Westinghouse AN/ALQ-105 electronic countermeasures were permanently installed in two long blisters on the underside of the aircraft. Thirty aircraft were fitted with specially designed pylons to permit them to carry the AGM-78 Standard anti-radiation missile, a considerable improvement over the somewhat lackluster Shrike. On a typical mission, the F-105G carried two Shrikes on outboard pylons, a single Standard on an inboard pylon balanced by a 450 US gallon fuel tank on the other side, and a 650 US gallon centerline fuel tank. The Wild Weasel aircraft were usually the first to arrive into the target area and the last to leave, staying after the strike to support rescue of downed aircrews. As such, fuel was a precious commodity and it was not uncommon for a Wild Weasel to require a 30-minute leave for aerial refueling in order to continue its mission.

Although the F-105D was withdrawn from Vietnam in 1970, the Wild Weasel aircraft soldiered on until the end of the war. They were gradually replaced by the F-4G Wild Weasel IV variant of the Phantom II.

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Medal of Honor recipients

The heroism of Thunderchief crews is exemplified in two Wild Weasel pilots receiving the Medal of Honor.

USAF Captain Merlyn H. Dethlefsen was awarded the Medal of Honor and Capt Kevin "Mike" Gilroy the Air Force Cross for an F-105F Wild Weasel mission on 10 March 1967 <ref>Template:Cite web</ref>.

USAF Captain Leo K. Thorsness was awarded the Medal of Honor and Capt Harold Johnson the Air Force Cross for an F-105F Wild Weasel mission on 19 April 1967 <ref>Template:Cite web</ref><ref>Audio excerpts and transcript of Maj Thorsness and Capt Johnson's mission on Wikisource</ref>.

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Flying the F-105

The initial reaction of the fighter pilot community to their new mount was lukewarm. Between its massive dimensions and troubled early service life, the aircraft had garnered a number of uncomplimentary nicknames. In addition to the aforementioned Thud, it was also the "Squat Bomber" and the "Hyper Hog." With time, the F-105s responsive controls, excellent performance at high speed and low altitude, and sophisticated electronics won over ever some F-104 Starfighter pilots. The "Thud" became a term of respect and endearment to the point where the F-84F Thunderflash became known as the "Thud's Mother."

Former Wild Weasel pilot Jerry Noel Hoblit recalled the awe of the F-105's size after transitioning to it from the F-86 Sabre, and he was unable to reach the air intake lip even with a running jump <ref name="Higham">Template:Cite book</ref>. Nevertheless, the F-105 had a spacious cockpit with a good layout (particularly after introduction of "tape" instruments) and visibility (except to the rear), and the complex electronics were easy to learn and operate. With high wing loading, the Thunderchief was by all acounts an excellent aircraft to fly at high speeds. Takeoffs and landings were often performed in the 230 mph (370 km/h) range. The spoliers 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 exahust 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 Thunderchief was rapidly withdrawn from USAF service after the end of the Vietnam War. Some aircraft remained in service with Air National Guard units, but their heavy wartime service meant that many F-105s had already reached or exceeded their service lives by the mid-1970s. The Thunderchief was officially retired on 25 February 1984.

Specially modified F-105Bs briefly flew with the USAF Thunderbirds demonstration team in 1964 until a fatal accident from overstressing the airframe forced a switch back to the F-100 Super Sabre after only six shows.

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Variants

YF-105A - Two pre-production prototypes.
YF-105B - Four pre-production aircraft.
F-105B - Initial production model; 75 built.
JF-105B - Test aircraft re-built from RF-105B airframes; 3 converted
RF-105B - Proposed reconnaissance version of the F-105B; none built.
F-105C - Proposed dual-control trainer; cancelled in 1957, none built
F-105D - definitive production model, all-weather capability thanks to advanced avionics, first flight 9 June 1959; 610 built.
RF-105D - Proposed reconnaissance version of the F-105D; none built.
F-105E - Proposed trainer version of F-105D; cancelled in 1959, none completed
F-105F - Two-seat trainer version of F-105D, fully combat-capable, first flight 11 June 1963; 143 built.
EF-105F - Initial SEAD/Wild Weasel version; 86 built.
F-105G - Two-seat Wild Weasel SEAD version, 61 converted from EF-105F and F-105F.