The F-105 Thunderchief was an American supersonic fighter-bomber that served during the Vietnam War. Originally an advanced derivative of the RF-84F Thunderflash, the F-105 was a large attack aircraft designed for both nuclear and conventional strike. F-105s would see extensive service in Vietnam as the USAF’s primary attack aircraft until high loss rates forced it to be retired from active service. A total of 833 aircraft were built.
A Repurposed Thunderflash — The F-105's Origins
The F-105 originated as an internal project of the RF-84F Thunderflash photo-reconnaissance aircraft, featuring the same wing-mounted engine intake system. First begun in 1951, initial design work resembled an enlarged RF-84 with an integral bomb bay in the middle of the aircraft. F-84Gs in Tactical Air Command service had been the first fighter aircraft in the world able to carry nuclear bombs, and the first aircraft able to conduct in-flight refuelling — and one of the few aircraft designed to be able to refuel by both probe-and-drogue and boom systems. However, this aircraft had merely been an interim while TAC waited for the F-84F to enter production, and as such, it was based on a previous variant — the F-84E, but also incorporated many of the technologies expected to be on the F-variant.
While the E/G variants closely resembled the F-84B in general shape, the F-84F was a radical departure, incorporating a high sweepback and more hardpoints for increased weapons carriage. The RF-84F was an even more radical departure from the previously established F-84 formula, including wing root intakes and a rounded nose for the cameras that it was required to carry in its photoreconnaissance role.
While the F-84G and F enjoyed success in Korea and in peacetime European service, Republic Aviation started a new project for a much-improved aircraft based on the RF-84F’s design work. Incorporating the same nose shape but with a radar inside, an enlarged centre-section capable of internally carrying a nuclear bomb, and incorporating the same wing-root intakes, the aircraft design called “Advanced Project No.63” (AP-63) resembled a much-enlarged RF-84.
Teething Problems and Shattering Expectations — The F-105's Early Years
Contracts for low-rate initial production were awarded to Republic in 1952 and 1953 for a total of 199 aircraft, with initial delivery scheduled for 1955. However, shifting requirements for the aircraft resulted in the project being delayed and contracts being cancelled until a solid contract was signed in February 1955 for 15 aircraft. This included two “YF-105A” evaluation aircraft, three “RF-105B” reconnaissance aircraft, and ten production “F-105Bs”.
In a testament to the survivability of the aircraft that would be proven later in combat, the first F-105B’s landing gear failed to extend during the end of its first flight due to suction that kept the gear bay doors sealed shut. The pilot had to belly in, which he did with considerable skill, and funnily enough, when he walked away from the aircraft, the Thunderchief belatedly popped its landing-gear doors open. The aircraft in question was repaired and back in the air within six weeks.
The USAF Tactical Air Command (TAC) had a full squadron of Thunderchiefs in service by mid-1959. On 11 December 1959, Brigadier General Joseph Moore, commander of the 4th Tactical Fighter Wing, set a world speed record of 1,958.53 km/h (1,216 mph) over a 100 km closed course in an F-105B. During testing in June of 1961, the F-105 delivered 7 tons of bombs, the largest bombload ever carried by a single-engine fighter.
In the spring of 1964, the Thunderbirds aerobatics display group, looking for a new high-performance jet to replace their F-100As, chose the F-105B as their mount. After modifying the aircraft to suit their needs, including strengthening the airframe, the F-105 would go on to perform in only six airshows before being pulled out of their service in favour of F-100s. During the final airshow, in a “pitch up” manoeuvre, an F-105 piloted by Cpt. Gene Devlins simply disintegrated mid-air, forcing the Air Force to re-evaluate the Thunderchief’s use by the aerobatics team, subsequently replacing their F-105Bs with F-100D Super Sabres.
F-105Bs would be entirely retired by the end of 1965, and the much-improved F-105D would replace them, which also incorporated strengthened wing spars. Project “Look Alike” would endeavour to fix problems with the routing of wires, mechanical cables and hydraulics piping, and would be implemented in 1962-1964 on the Thunderchief fleet, just in time for their combat service in Vietnam.
Rolling into Combat — Operation Rolling Thunder & Vietnam
The F-105 would soon see active combat in the Vietnam War, where it served as the USAF’s primary attack aircraft. The F-105s would eventually fly over 20,000 combat missions in Vietnam, and despite its large and unwieldy airframe, shoot down 27 Vietnamese MiGs. 24 of these aircraft were shot down using the F-105's internal Vulcan cannon.
However, F-105s in Vietnam suffered from an extremely high loss rate. The F-105 had the unfortunate distinction of being the only American aircraft to have been removed from combat due to high loss rates, being replaced in its ground attack role by the F-4 Phantom II and F-111 Aardvark. Of 833 total F-105s produced, 382 aircraft were lost: 17 to enemy fighters, but mostly to ground anti-aircraft fire and maintenance issues.
This loss rate, however, is less indicative of the aircraft’s ability, but more a testament to doctrine and the aircraft’s environment. The F-105 was the most-used aircraft during Operation Rolling Thunder — even more so than the F-4C that had only recently entered service. Given that the aircraft flew the most sorties, it was also the aircraft that would, naturally, take the most losses. Due to the rate at which aircraft were being thrown against the Vietnamese air defenses, the aircraft suffered correspondingly high losses to the point that the US Air Force contemplated restarting the F-105 production line in Farmingdale, Long Island, but ultimately decided against it, as there were no export customers for the aircraft, and there were replacements just over the horizon — including the results of the TFX program, the soon-to-be-famous F-111.
Ground anti-aircraft fire was an inevitable part of flying into an air defence system. Designed to fly low and fast attack profiles, with not many provisions for high-altitude bombing, the F-105 needed to dive-bomb its targets with conventional bombs, with the pilot required to keep the target in sight of a depressible mil sight in the cockpit at all times. This resulted in pilots being forced into low, slow, and fatally predictable flight profiles when entering a bomb drop. The arc that the F-105s would fly in order to get close in to the target was an extremely easy target for Vietnamese anti-aircraft gunners. While the “Thunderstick-II” upgrade, developed in the late '60s, would allow the F-105 to bomb its targets from higher up using a set of new avionics that went in a spinal bulge (much like the MiG-21SMT’s spine fuel tank), these aircraft, mostly older D-5 and D-10 models, would never see combat, and the upgrades were deemed too costly to roll out to the entire remaining number of F-105s available, which were all soon to retire.
The most common technical issues were related to the F-105's J75 engine, which simply had not been designed for missions in the envelopes that the F-105s were expected to fly, burning at full military power for extended periods of time without overhaul. Since the F-105 had been designed with the Tactical Nuclear Strike role in mind, with its afterburners on full in what was essentially a one-way suicide mission, it had been designed to be the fastest thing flying with a nuclear bomb inside the ventral bomb bay.
The J75 had not been designed with long operating hours in mind, since the expectation had been that it would be used a few times in combat prior to being either shot down, disposed of, or otherwise never used again. This resulted in many issues with the jet blades, including cracks in the compressor blades that turned the inside of the engine into a mess of hot metal where the fragmenting blades would shatter, spreading fragments backwards into the engine as they went, causing what appeared to the pilot as a mere engine fire, but was only the precursor to a violent explosion when the fragmenting blades set fire to the initially completely unprotected fuel tanks.
The fuel tanks had been another oversight in the F-105's design — the initial flight profile of low-altitude tactical nuclear strike did not have high projected survivability rates, and for the sake of speed and also the fact that the F-105 wasn’t likely to return anyway, the aircraft’s massive fuselage fuel tanks, arranged above the engine and bomb bay, were not self-sealing. Many flak and SAM losses due to fires stemmed from the punctured fuel tanks leaking fuel all over the hot J75 engine, resulting in the aircraft burning down in flight. Upgrades to the fuel tank, including the addition of self-sealing liners, managed to somewhat rectify, but never completely solve, the issue — no upgrade save for a complete redesign would solve the fact that the F-105's entire internal fuel load was carried in tanks that were mounted in the top of the fuselage and above the engine.
Another issue encountered was that sudden loss of hydraulic oil pressure resulted in the tailplane locking into a “pitch down” position, as well as losing the Stability Augmentation system, a vital component of such a large, heavy aircraft that allowed pilots to keep it under control. A switch was later added to mechanically lock the F-105's tailplane into a stable, “neutral” position, but again, this was only a partial fix — the hydraulics issue would never really be overcome throughout its service life.
Sunset Service
Aircraft of the F-105G “Wild Weasel” suppression of enemy air defence (SEAD) variant remained in service until the end of the Vietnam War, after which they were replaced by the F-4G Wild Weasel IV. F-105s grew increasingly difficult to maintain in the 1970s, resulting in their accelerated retirement. The last F-105Ds in South-East Asia left by 1970, before Operation Linebacker began, and twin-seat F-105Fs and Gs would soldier on into the '80s before retiring. The final flight of any F-105 was by the Air Force Reserve 466th Tactical Fighter Squadron, in 1984, and afterwards, the F-105 slipped quietly into retirement.
Most F-105s had their tails sliced off by guillotine to prevent their use elsewhere. 105 complete F-105 airframes are known to survive to this day, though none remain airworthy. Most are in the continental US, though a few remain in places like Nellis, McConnel, Kadena, and Spangdahlem as monuments to when Thuds were deployed to those bases. The rest are in museums and other such places to live out the rest of their lives as retired warbirds.
