There was talk about canceling the F-105D program because of several groundings of the fleet following engine problems that resulted in two fatal accidents
The F-105 Thunderchief originated from a 1951 effort to find a replacement for the F-84F fighter-bomber. Its prototype took to the air for the first time in October 1955, and Republic handed over the first operational aircraft to the U.S. Air Force (USAF) in 1958.
By the mid-1950s, Tactical Air Command wanted something no fighter-bomber had yet delivered: a single-seat aircraft that could cross Europe at treetop height, carry a nuclear weapon at supersonic speed, and make it home again. The swept-wing F-84F, itself a stretched version of a Korean War straight-wing veteran, could not do the job. Republic answered with a big, narrow-fuselage machine powered by a Pratt & Whitney J75 engine variant and thrust, and designed around one priority: speed. That choice gave the F-105 its performance. It also gave it an appetite for fuel, maintenance hours, and runway. On paper it was spectacular. The crews who had to keep it flying would learn the cost of that ambition the hard way.
The F-105D model—of which the first example flew on June 9, 1959, with a total of 610 eventually produced—was an all-weather fighter-bomber variant. It was equipped with monopulse and Doppler radar systems, enabling operations at night and in poor weather conditions. The original internal weapons bay, initially intended to carry nuclear ordnance, was closed off and repurposed to house extra fuel tanks. Conventional bombs were instead mounted on multiple ejector racks along the fuselage centerline and on underwing pylons. The aircraft was also outfitted with a retractable probe for aerial refueling.
Why the F-105D Program Nearly Ended
However, despite these advantages, there were discussions about terminating the F-105D program after repeated fleet groundings caused by engine problems, resulting in two fatal crashes.
According to Ted Spitzmiller’s book Century Series: The USAF Quest for Air Supremacy 1950–1960, as with earlier F-105 versions, the use of production blocks created configuration differences that complicated maintenance procedures and spare parts ordering. In particular, issues with routing and securing the extensive wiring, along with the hydraulic and fuel lines, led to chafing, which in turn caused electrical shorts and fluid leaks, driving up maintenance demands and contributing to several accidents.
Project Look-Alike, Sealed Panels and Safety Pack II
To address these problems, the Air Force implemented a standardization initiative known as “Project Look-Alike” between 1962 and 1964 to inspect and correct these systems.
In addition, steps were taken to resolve the issue of water seeping into various small gaps and cavities in the airframe, which was causing serious electronic failures and other maintenance difficulties. This problem became especially apparent during deployments in Europe, where seasonal weather conditions were much harsher. Once access panels were properly sealed and the aircraft were coated with a silver lacquer to protect as much of the surface as possible, the frequency of these failures declined.
Another recurring issue involved excessive heat in the afterburner (AB) section of the fuselage. To fix this, engineers added two extra air inlets on each side of the rear fuselage, allowing more outside air to flow in and cool the area.
Howard Plunkett, author of the book F-105 Thunderchiefs: A 29-Year Illustrated Operational History, with Individual Accounts of the 103 Surviving Fighter Bombers, says, “A ‘constant problem’ is a bit understated. Fuel leaks and overheating caused explosions and aircraft losses. Safety Pack II was the mod that installed the cooling scoops on the left fuselage, among other things, during March–July 1965. It was probably the most significant mod to the F-105 and fixed the problem in time for combat deployments that year.”
Because of all these issues, the initial plan to build 1,500 aircraft was sharply reduced.
The F-105 by the Numbers
The figures tell the story better than any press release. Republic built 610 F-105Ds, and the first one flew on June 9, 1959. The Air Force had once planned on 1,500 aircraft, a number the groundings and fixes cut sharply. It took the standardization effort of Project Look-Alike, from 1962 to 1964, and then Safety Pack II, from March to July 1965, to tame the wiring, fuel, and heat problems. At roughly 50,000 pounds (22,700 kg) of metal, the Thud was the heaviest fighter of its era, and its high wing loading meant it dropped rapidly when the engine failed. By the end of the Vietnam War, the F-105 had paid for its reputation in blood: total F-105 losses in Southeast Asia, commonly cited as about 395–400 of 833 built.
How the F-105 Became the “Thud”
In the end, as Spitzmiller recounts, although “Thunderchief” sounded impressive to Republic and its public relations team, the pilots who flew this heaviest fighter of its era—whose high wing loading meant it dropped rapidly if the engine failed—gave it a different nickname. Whether inspired by the crash of 50,000 pounds of metal slamming into the ground or as a playful shortening of the name of Howdy Doody’s TV adversary, Chief Thunderthud, the F-105 was affectionately dubbed the “Thud” by the aircrews and maintainers who worked with it.
The nickname stuck because it was honest. “Thunderchief” belonged to the brochure; “Thud” belonged to the men who knew what the airplane could do to them. Yet the same crews who coined it flew the F-105 into some of the most heavily defended airspace of the Vietnam War, and the fixes that came out of those early groundings are part of why it got there at all. A fighter that nearly lost its program became a legend of Rolling Thunder, and its name, half insult and half badge of honor, outlasts every press release Republic ever wrote.
F-105 Thud FAQ
Why was the F-105 called the Thud? According to Ted Spitzmiller, aircrews and maintainers coined it, either from the sound of a heavy aircraft hitting the ground or as a short form of Chief Thunderthud, the Howdy Doody character. Both explanations are widely repeated, and nobody has settled which came first.
Was the F-105D really almost canceled? Repeated groundings after engine problems that led to two fatal crashes prompted discussion about terminating the program. The initial plan to build 1,500 aircraft was sharply reduced, and the fixes that followed, from Project Look-Alike to Safety Pack II, kept the F-105D in production and ready for combat deployments in 1965.
What fixed the F-105D’s overheating problem? Extra air inlets on each side of the rear fuselage let outside air cool the afterburner section. Howard Plunkett credits Safety Pack II (March–July 1965) as probably the most significant modification the F-105 received, and it arrived in time for combat deployments that year.
Century Series: The USAF Quest for Air Supremacy, 1950-1960 is published by Schiffer Publishing and is available to order here.
Photo by U.S. Air Force
