The Republic F-105 Thunderchief
Copyright ©2002 Tor Willy Austerslått
Also published on Everything2
If you had been on the ground somewhere in the Vietnam War and looked skywards upon hearing the roar of jet engines, the odds of it being a flight of F-105 Thunderchiefs would have been good. The F-105 was beyond comparison the most numerous aircraft to streak across the skies of Vietnam in the 1960's. Also beyond comparison, it fell out of the East Asia skies in larger number than any aircraft since World War II.Background
The F-105 was designed from the beginning as a supersonic tactical nuclear fighter-bomber. If you think about it, it's a rather narrow mission for an expensive aircraft. However, when the US Air Force in 1950 asked Republic to initiate the design studies for it, things were very different. The US Air Force inventory was not just bigger in number of aircraft, but it had aircraft types for every conceivable mission any commander could think of. The F-105's part in this was simple: fly at supersonic speeds at low levels, deliver a single tactical nuclear weapon on the battlefield and get the hell away from the blast. Multirole or swing-role aircraft like we know them today in the shapes of the F-16, F/A-18 and the Eurofighter Typhoon was unheard of, mainly for technical reasons.
Intended to replace the F-84F Thunderstreak which was an adaptation of a fighter into a fighter-bomber, the pure fighter-bomber F-105 got a very large interior bomb bay. The bomb bay was designed to accomodate a single tactical nuke, and because of the bomb bay the Thud was at that time the largest single-engine single-seat fighter ever built.
In May 1952 the US Air Force officially endorsed Republic's swept-wing design, applying the designation F-105 to it. The first of 199 ordered aircraft was supposed to be ready for service in 1955.
In March 1953, the Korean War was expected to shortly come to an end, leaving the F-105 without any mission to fulfill. Being unable to think up any other operational requirements, the US Air Force changed the order to nine RF-105A photo reconnaissance aircraft and 37 regular F-105A fighter-bombers.
The Thud was a large and heavy aircraft. It was in fact so large and heavy that when the US Air Force went to Farmingdale, New York to inspect a mock-up of it, it was obvious to anyone present that the proposed Allison J-71 turbojet engine would not be up to the task of pushing it through the sonic wall. It was decided to instead go for the more advanced Pratt & Whitney J75 turbojet engine. Since the J75 wouldn't be available for a couple of years, there would now be two F-105 variants; the F-105A with a Pratt & Whitney J57 engine and later the F-105B with a Pratt & Whitney J75 engine. A subtle difference in name, but a huge difference in performance.
Republic F-105D Thunderchief. Photo: USAF
After a long period of backs and forths regarding the US Air Force's contract with Republic, delays building the prototype and the industry-wide discovery of the area rule, the first YF-105A was ready for its maiden flight over the Mojave Desert on October 22nd, 1955. Behind the stick was Republic test pilot Russell M. Roth. Even with the J57 engine and a fuselage designed without the aforementioned area rule, the prototype attained Mach 1.2 in level flight. The first prototype was destroyed in a crash in December 1955. The second identical prototype took to the air on January 28, 1956.
On June 19th, 1956, the F-105 was officially given the name "Thunderchief", following a long tradition of giving Republic aircraft names beginning with "Thunder". The most well known of the Thud's predecessors is perhaps the WWII-era Republic P-47 Thunderbolt.
The YF-105B prototype flew for the first time on May 26, 1956, and the first F-105B production aircraft took off on May 14, 1957. The differences from the YF-105A were many; a larger tailfin with an air intake in the root and forward swept engine air inlets in the wing roots. The ram-air intake in the tail fin root provided cooling for the MA-8 firing control system, E-34 radar ranging gunsight and the E-30 bombing computer, all of which hadn't been present in the F-105A.
From Republic's plant in Farmingdale, New York, production F-105B's began emerging in 1958. Despite a rash of problems with spare parts, the autopilot and the fire control system, the F-105B completed its first year in operational service without any major accidents. No other US military aircraft had accomplished that before.
Many aircraft get derogatory nicknames, the F-105 being no exception. The sheer size and weight of the F-105 coupled with the design decision to use only one engine, led to the name "Thud". This was supposed to be the sound it made when it crashed to the ground shortly after takeoff. Other nicknames included "Ultra Hog", "Super Hog" and "Lead Sled".
The USAF Thunderbirds
On December 11, 1959, an F-105B piloted by Brigadier General Joseph Moore set a new world speed record of 1216.48 mph/1957.31 km/h over a 100-kilometer closed circuit. Four days later this record was beaten by a Convair F-106 Delta Dart flying at 1525 mph over Edwards AFB in California.
In spite of its weight and size, the USAF Thunderbirds aerial demonstration team selected the F-105B to do their aerobatic manoeuvers, replacing the much smaller and agile F-100C Super Sabre. The Thunderbirds took delivery of nine specially modified Thuds, just days before their scheduled appearance in their new mounts. The Thuds lasted only a few months and six airshows with the Thunderbirds. After an accident in which one of the pilots was killed, the Thunderbirds were again equipped with Super Sabres, this time the F-100D
In response to the Gulf of Tonkin Incident in August 1964, eight F-105D's were sent from Yokota AFB in Japan to Korat RTAFB in Thailand. A unit of F-105's were deployed to Da Nang in Vietnam the same month, but the majority of Thud operations were conducted from Korat and Thakli air bases in Thailand. The main reasons for stationing Thuds in Thailand was space; air bases in Vietnam were generally crowded and very busy.
When the US engagement in Vietnam ended, Thuds had flown 75% of all bombing missions over North Vietnam. During operation Rolling Thunder (March 2, 1965 - October 31, 1968), the Thud was USAF's primary strike aircraft, penetrating deeper and deeper into North Vietnamese airspace as Rolling Thunder progressed. The reasons for this are quite obvious; it could fly fast, it could take a serious punch without falling apart and it could carry a large amount of bombs. The internal bomb bay of the Thud would usually be fitted with a 365 U.S. gallons internal fuel tank, leaving only the five wing and fuselage hardpoints for ordnance. These, however, could accomodate 6350 kgs of conventional or napalm bombs. A Thud was commonly loaded with up to 16 M117 750 lb. bombs.
196 USAF pilots lost their lives flying the Thud between April 1965 and September 1972. In over 20,000 missions flown, 397 Thuds were lost, mostly to enemy anti-aircraft fire and surface-to-air missiles. In all, nearly half of the 833 F-105's built were lost in combat or accidents. Thuds were credited with shooting down 27.5 enemy aircraft in their secondary air-to-air role, utilizing both the internal 20mm gun and AIM-9 Sidewinders, of which the Thud could carry up to four.
In Colonel (ret.) Jack Broughton's book Thud Ridge, it is described like this:Thud Ridge: The string of small mountains that stretches like a long bony finger pointing at Hanoi is known as Thud Ridge. It was one of the few easily identifiable landmarks in the hostile North, marking the route to the modern fighter pilot's private comer of hell - the fiercest defenses in the history of aerial warfare and the targets of downtown Hanoi.
Thud Ridge were easily spotted on weather satellite photos, and thus pinpointed the weather in the Hanoi area - the infamous Pak Six or Route Package Six. It was also the most heavily defended area known to man; surface-to-air missile systems, ground radars, anti-aircraft guns and thousands of small arms on the ground made it a nightmare for fighter pilots trying to make it to their targets.
After bombing of North Vietnamese targets commenced in August 1964, US aircraft losses were mounting at an alarming rate. The majority of losses were to radar-guided SAM missiles. The USAF decided that the best tactic was simply to hunt down enemy radar installations and put them out of play. To do this, a project named Wild Weasel was started, equipping F-100F Super Sabres with electronics to determine the location of enemy radar installations. Aircraft accompanying the F-100F's would attack the radar site with conventional bombs once it had been pinpointed by the Wild Weasel aircraft. The name Wild Weasel was taken from the Weasel, which is known to fearlessly pursue its prey into its den.
Once the Wild Weasel concept had proven itself, 86 F-105F two-seaters were converted from trainers to Wild Weasel III aircraft. Eventually, these two seaters was designated F-105G. The rear seat EWO (Electronic Weapons Officer) operated an array of electronic equipment that could pinpoint the location of enemy radars and attack them with AGM-45 Shrike anti radiation missiles. The Wild Weasel III aircraft also had powerful jamming equipment that would confuse missiles once fired, and could alternatively direct other aicraft to the radar site to destroy it. The first Wild Weasel III missions were flown in June 1966, and although the loss of other aircraft dropped, eleven of the F-105G's had been lost at the end of August the same year.
- YF-105A: Original prototype, never went into production
- YF-105B: Improved prototype with upgraded engine and new fuselage shape dictated by the area rule
- F-105B: First production one-seat fighter-bomber; 71 built
- RF-105B: Proposed reconnaissance model, never built
- JF-105B: Test aircraft re-built from RF-105B airframes; 3 converted
- F-105C: Proposed two-seat trainer, never built
- F-105D: One-seat all-weather fighter bomber with new radar and navigation equipment, improved engine, and better avionics; 600 built
- RF-105D: Proposed reconnaissance model, never built
- F-105E: Proposed two-seat trainer based on the 'D' model, never built
- F-105F: Two-seat combat-capable trainer; 143 built
- EF-105F: Rebuilt 'F' models equipped with radar homing and jamming equipment; 86 converted
- F-105G: Two-seat Wild Weasel SEAD model with ECM, radar homing, and jamming equipment; 60 EF-105F models rebuilt as 'G' variant
Goodbye to the Thuds
Between 1961 and 1968, the Thud was stationed at Bitburg AB (36th Tactical Fighter Wing) and Spangdahlem AB (49th Tactical Fighter Wing) in Germany. Until 1970, USAFE used Wheelus AB in Libya amongst many other things as a training ground for European air crews. The fighter wings from the 36th and 49th temporarily dispatched to Wheelus for bombing and gunnery training throughout the 1960's. In 1986 the former Wheelus AB (now Okba Ben Nafi AB) was bombed by aircraft from USAFE in Operation El Dorado Canyon.
Following the end of the Vietnam War, Thuds were handed over to the Air National Guard (ANG) in the continental USA. The last operational sortie was flown by the Georgia ANG on February 25th, 1984. A number of Thuds have survived in museums and as gate guards on various air bases around the world.
Pak Six, A True Story. Gene I. Basel, ISBN 0-515-09005-0. Memoirs of a 78 1/2 mission Thud pilot in the Vietnam war.
When Thunder Rolled. Ed Rasimus, ISBN 1-588-34103-8. Memoirs of a 100 mission Thud pilot.