Air University Review, January-February 1983

Thunderchief

Theodore Van Geffen, Jr.
Senior Master Sergeant Gerald C. Arruda

A JOKE in the early sixties had the F-105 used as a squat bomber; taxi over the enemy tank, retract the landing gear, and log the kill. Early crews dubbed it the Lead-Sled and Ultra-Hog. In fact, it took a war to erase such negative reactions. The F-105’s high speed at low altitude, its flight stability at all speeds, and its ability to haul a heavy bomb load proved to be great assets in the Vietnam War. If any single factor won over even the hardest-to-convince, it was the aircraft’s ruggedness that enabled it to sustain extensive battle damage and return the pilot to friendly territory, an ability owed largely to its tough J75 engine and dry wing.* Ever since, everyone involved with the F-105 has called it by the affectionate nickname Thud.

*The F-105 wing, unlike that of many contemporary aircaft, contained no fuel tanks, thus sharply reducing the vulnerability area of the aircraft.

Some years before the F-84F Thunderstreak entered the U.S. Air Force inventory, fifteen engineers at Republic Aircraft Corporation had conceived, as a private venture, model Advanced Project (AP) 63-31 to improve the performance of and succeed the F-84F series. Numerous configurations were investigated after which Republic decided that the basic concept should be a single-seat, single-engine aircraft, primarily meant for the nuclear mission but with secondary air-to-air capabilities. The F-105’s projected nuclear role was to result in an unplanned benefit designed to carry a single nuclear weapon, the F-105 was built with an internal bomb bay, an unheard of design feature for a fighter. Although the bomb bay never carried a bomb into combat, it provided secure storage for a fuel tank which gave the Thud extra range without a drag penalty. In February 1952, Republic proposed the new airplane, initially designated Weapon System 306A, to the Department of Defense (DOD). Altogether the development would embrace 5,000,000 manhours of study over a six-year period.

As recommended by the Aircraft and Weapon Board, the Air Staff endorsed the F-105 in May of 1952 instead of ordering an improved version of the F-84F. Five months later, on 25 September, Republic received a contract directing it to proceed only with the preproduction engineering, tooling, tool designing, and material procurement needed for tentative production. Fabrication and material procurement originally called for the acquisition of 199 aircraft with the first Thunderchief operational by 1955. Following a configuration conference on 16 February 1953, the final shape of the F-105 became evident. In May, the Air Research and Development Command (ARDC) advised that it was programming the T-171-D Gatling-type gun for eventual use in the F-105. In June, the preliminary model specifications were completed and approved by Hq USAF.

In the meantime, however, a change of plans announced in March had reduced the initial number of aircraft from 199 to 46, including 37 F-105s and 9 RF-105s. In an August 1953 warning, the National Advisory Committee for Aeronautics informed Republic that the overall efficiency of the J-71 engine was only 80 percent of that predicted by the contractor. Interim use of the Pratt & Whitney J57 engine was then considered. Despite this setback, delivery of the first aircraft was still scheduled for the spring of 1955.

The beginning of 1954 did not look bright for the further development of the F-105. At one point, the Air Force suspended procurement of the aircraft because of excessive delays at Republic. However, in late February, the Air Force decided to procure 15 aircraft after all, to be powered by the interim Pratt & Whitney J57-P-25 with 16,000-pound thrust, as recommended by the Wright Air Development Center (WADC). In May, a provision was made to install the M-1 and MA-i bomb computers in the event that the development of the long-range toss bomb computer and the MA-8 time-of-flight computer lagged.

Development of the F-105 was still shaky when, on 10 August 1954, the Air Force authorized the modification of four F-105s "as required to incorporate the YJ75-P-1 in lieu of the J57-P-25 engine." One month later the Air Force, because of further development slippages, decided to reduce the program to only three aircraft. But within a month, the F-105 program was revised yet another time to provide for six aircraft, two powered with the J57 and the remaining four with the J75. In December, General Operational Requirement (GOR) 49, calling for in-flight refueling capability, a more complex fire-control system, and improved performance, was approved. Finally, the GOR dictated that the higher-thrust J75 engine be installed to qualify the fighter-bomber for first-line service from 1958 through the sixties. This did not halt further changes; GOR 49 was revised three more times between December 1954 and April 1955.

The F-105 design team headed by Alexander Kartveli, famous as the designer of the P-47 Thunderbolt, constantly proposed new design features. Among the most striking was the "coke bottle" shape of the fuselage, reflecting the "area rule" design principle.* Other innovations included the swept-forward air-intake ducts, a ram-air intake, "clover leaf" speed brakes, and a one-piece, fully maneuverable flying tail. As construction of the first two F-105s was too far advanced to incorporate these innovations, it was obvious that the third F-105 featured substantial external modifications. Meanwhile, in February 1955, an amendment to the August 1954 contract again authorized the acquisition of fifteen test aircraft funded in February 1954 and changed the funded F-105 procurement to include two YF-105As (with J57 engines), ten F-105Bs, and three RF-105Bs. Seven months later, on 19 September, the parts of the first YF-105A were delivered from Republic’s Farmingdale plant in Long Island, New York, to Edwards AFB, California. After assembly, the Air Force conducted a safety inspection on 13 and 14 October and two days later tested the engine. Finally, on 22 October, Republic’s chief test pilot, Russell "Rusty" Roth took the YF-105A for a 45-minute flight, during which time he managed to exceed mach 1 despite the limited power of the J57 engine.

*The area rule, for which no theoretical explanation existed at the time, dictated that transonic speeds could not easily be exceeded unless an aircraft's total cross-sectional area changed smoothly from nose to tail. For the F-105, this meant that the fuselage had to be pinched in sharply at the wing roots to compensate for the large wing, then expanded behind the wings to smooth the transition.

By mid-November, the prototype had accumulated 12 flights and adequately demonstrated airworthiness. On the last day of that month, the Air Force accepted the aircraft and turned around to bail it back to Republic for Phase I flight testing. Fifteen days later, however, after 22 hours of flight time and on its 29th flight, the YF-105A made a wheels-up landing on a dry lake bed at Edwards. It was immediately awarded "aircraft out of commission" status and returned to the factory.

On 28 January 1956, the second YF-105A, also powered by the J57, made its maiden flight and was accepted by the Air Force three days later. On 19 February, the production of the F-105 suffered another setback when machinists at Republic went on strike, staying out for nearly four months. As if to compensate for these frustrating delays, in early 1956, at Edwards AFB, the F-105 was named overall winner in a competitive flyoff against the North American XF-107, a J75-powered derivative of the F-100 Super Sabre.

Meanwhile, on 14 March, Republic received the first J75 engine on schedule, which together with the first Republic YF-105B was airlifted to Edwards AFB on 29 April. Also in March, the Air Force released $10 million of FY57 funds for the acquisition of 65 F-l05Bs and 17 RF-105Bs. The first flight of the YF-105B took place on 26 May. The flight ended in a wheels-up landing with only minor damage, caused by the inability to lower the nose gear. This resulted in a further delay of the test program. The first YF-105B was finally accepted by the Air Force on 31 August. By July, the Air Force had decided that it preferred the RF-101C Voodoo to the reconnaissance version of the F-105, and the three RF-l05Bs already on the assembly line were canceled and were completed asJF-l05Bs. The 17 RF-105s funded from FY57 funds were also canceled. (In June. five F-105Cs, a tandem seat version of the F-105B, had been added to the program, but these were canceled on 30 October 1957.) In August 1956, the F-105 was officially named the Thunderchief. By 30 June 1957, Republic had completed only five aircraft, two YF-l05As and three YF-105Bs.

On 8 July, Hq Air Materiel Command (AMC) announced plans to equip the F-105 with an AN/APN-105 Doppler navigation system, deleting the planned inertial navigation system. At about this time, all F-105 requirements were consolidated in a completely revised GOR 49, including as new requirements the Doppler system, a cockpit instrument display, a tow target subsystem, and a TX-43 nuclear delivery system.

The first production model of the F-105 was accepted on 27 May 1958 and entered operational service with the 335th Tactical Fighter Squadron/4th Tactical Fighter Wing at Eglin AFB, Florida, in August three years later than originally planned. By mid-1959, the Tactical Air Command possessed only one complete squadron of 18 F-l05Bs. Because of difficulties enumerated, Category I, II, and III flight tests were either delayed or interrupted: Category II testing was extended beyond the 30 November 1959 deadline and officially ended on 30 March 1960. Category II operational testing was accomplished by an operational unit, the 335th TFS at Eglin, in order to speed transition of aircraft from test to squadron use. During Category II testing under Project Fast Wind, Brigadier General Joseph H. Moore, Commander of the 4th TFW, set a new world’s speed record of 1216.48 mph at Edwards AFB for a 100 kilometer closed circuit without payload run. On 1 June, Category III test program for the F-105B started at Seymour-Johnson AFB, North Carolina, and ended on 16 August. However, despite the success of the modifications accomplished during the tests, the poor reliability of the MA-8 fire control system raised serious doubts as to the system’s overall capabilities. By 31 March 1960, TAC possessed 56 F-105Bs, none of which were operational.1

During 1960 and 1961, the aircraft in-commission rates remained low. F-105s were frequently grounded for want of spare parts and shortage of maintenance skills needed for attending to the increased complexity of the weapon system. It took about 150 maintenance hours to get the F-105 airborne for one hour.

Meanwhile, Republic was studying a new version of the Thunderchief, designated F-105D. It featured a higher-thrust J75-P-19W engine with water injection, bad-weather navigation system (ANP-131 Doppler), a Bendix toss-bomb computer, and integrated instruments (including the ASG-19 Thunder-stick fire control system with the North American Search and Ranging Radar/NASARR R-14A all-purpose monopulse radar). Altogether these devices formed the most sophisticated automatic navigation and aiming system then in existence.

Troubles plagued the F-l05 program throughout 1961. In December, certain F-105B/Ds were grounded for inspection after routine laboratory fatigue tests at Wright-Patterson AFB, Ohio, resulted in a failure of the aircraft’s main fuselage. Yet successive tests revealed that the frame retained considerable strength after cracking, and Republic moved quickly to correct the defects. The program, however, was still in trouble, and on 23 June 1962, Hq USAF grounded all F-105s after two were lost within eight days in major accidents at Nellis AFB, Nevada. The Air Force rescinded all flight restrictions on 12 October 1962 except those on the automatic instrument landing system.

Again, corrective actions had to be taken to save the F-105 program. Project "Look-Alike" was originally developed by the F-105 System Program Director (SPD) in January 1962, with the objective of standardizing all F-105Ds to a single configuration. The major work was originally planned over one or more years during normal maintenance cycles. The project was divided into two phases. In phase I flight safety modifications were made. In phase II the fleet was modernized and its combat capability enhanced. In May 1963, the Air Force ordered the most extensive and subsequently the most significant modification, installation of the dual in-flight refueling capability. This major structural modification to the nose of the aircraft took about 2000 hours per aircraft. The decision to incorporate this modification into the program extended the completion until May 1964.

In March 1959 the production program was changed once more. The Air Force canceled the high cost two-seat F-105E (the F-105E was a Republic Aviation Corporation proposal to the Air Force featuring a one-piece canopy over the tandem seats: the E models already on the line were converted to straight D models) in favor of a speed-up production of the F-105D. Altogether, 18 F-105Es would be affected in FY58, 1959, and 1960. On 9 June 1959, the F-105D made its debut flight at Farmingdale, and six months later the first F-105D arrived at Eglin AFB, Florida, for the second phase of testing.

After having entered service with TAC, USAFE’s 22d TFS/36th TFW at Bitburg AB, Germany, became the first unit outside CONUS to receive the F-105D, when on 12 May 1961 two F-105Ds landed there on the first high-flight mission. On 10 January 1964, the final F-105D delivery, the 610th, was delivered to McConnell AFB, Kansas, for service with the 23rd TFW.

Republic kept pushing the two-seat version of the F-105. In May 1962, Hq USAF decided to go ahead with the design of a two-seat Thunderchief to be designated F-105F and authorized the purchase of 36 F-105F aircraft with FY62 money and 107 additional F aircraft with FY63 money. However, the 36 F series airplanes, to be bought with FY62 funds, would replace a like number of F-105D aircraft. The F-105F featured a 31-inch longer fuselage to accommodate the second cockpit and a higher tail fin. Its first flight was made on 11 June 1963, forty days ahead of schedule. On 7 December 1963, the 4520th Combat Crew Training Wing at Nellis AFB received its first F-105F while the acquisition by the 4th Tactical Fighter Wing at Seymour-Johnson AFB, North Carolina, on 26 December signaled the start of operational service for the F-105F.

The F-105F, developed from the D model, did not require extensive testing. Category I and II testing took 15 months, from June 1963 to August 1964. The two-seater went through a series of tests to determine if the addition of a rear cockpit, radar, and other equipment had any adverse effect on the front-seat equipment and to see how closely the radar presentation in the rear seat duplicated that in the front. On the other hand, the F-105F retained the shortcomings of the F-105B/D and had to receive substantial safety modifications and improvements as well. The final F-105, an F-l05F, was delivered to Brookley AFB, Alabama, on 9 January 1965.

Another version of the F-105D was considered, although only on paper. That would have been the RF-105D. It would have been equipped with a variety of cameras and a pod containing side-looking radar and infrared sensors. Additionally, the RF-105D would have retained its strike capabilities. When the Air Force opted for the McDonnell RF-4C, the reconnaissance version of the Thunderchief was dropped (December 1961).

Unfortunately, despite the successful completion of the "Look-Alike" program, the F-105 was not as safe as the Air Force wanted it to be. During the first four months of 1964, twelve F-105s were lost in major accidents due to engine failures, fuel leaks, and malfunctions in the fuel venting systems. At the time, these causes were not readily apparent. Therefore, Tactical Air Command requested a program dubbed "Category X Test" to seek out the problems. Air Force Chief of Staff, General Curtis E. LeMay gave the tests top priority. Accordingly, the Category X people went over five F-105Ds in minute detail. Once the installation of simple but sensitive test instruments had been completed, each plane was taken out for a taxi test. When the results of those tests were known, test pilots put the aircraft through a series of increasingly difficult flights. The testers had 90 days to complete the program, but it took only sixty; thus, 500 flying hours were accumulated.

Accordingly, a major Class IV modification program, nicknamed "Safety Pack I and II," was accomplished on the F-105 fleet on 30 June 1965 and in May 1966, respectively. The modification provided major improvements in the basic fuel system, the plumbing, and incorporated provisions for increased ventilation and cooling in the engine shroud area.

More modifications and reconfigurations were to come for the Thunderchief. In the midsixties, the

war in Southeast Asia prompted an entirely different mission for the F-105: low-level penetration to attack with conventional weapons. To accomplish this mission, a score of major modifications were needed. A few were to improve mission reliability, but the majority were to change or enhance mission capability. Modifications included installation of AGM-12C/E Bullpup and AGM-45A Shrike capabilities, installation of QRC-160 electronic countermeasures pods under the wing, and provision for an X-band radar. Further modifications included installation of multiple ejector racks under the wings and fuselage so that the F-105 could carry a larger and more varied assortment of ordnance.

By late 1965, North Vietnamese surface-to-air missiles (SAMs) had become a serious threat, requiring the development of an electronic device to warn of Fansong (SA-2 associated radar) tracking, lock-on, and missile launch. Taking the equation a step further, the ability to locate and attack SAM sites was needed. Altogether there were twelve electronic countermeasures/quick reaction capability modifications. Among the most significant were the installation of radar homing and warning (RHAW) gear and the development of the Wild Weasel two-seat F-105F SAM hunter-killers. In January 1966, further modifications to the F-105F gave these Wild Weasels the ability to use AGM78A and AGM-78B, Standard antiradiation missiles (Standard Arm). Numerous other modifications resulted in a varied number of aircraft with peculiar configurations tailored for specific types of SEA missions, such as the specially modified F-105F Commando Nail all-weather attack planes featuring a modified radar and rearranged weapon release switch which enabled the back seater to control bomb release, and the F-105F Combat Martin communication jammer planes, featuring installation in the back seat of the QRC-1 28 VHF jammers to block communications between MiGs and their ground-control intercept centers. In fact, these QRC-l 28-equipped F-105Fs became one-seaters.

Combat experience gained in Southeast Asia resulted in the introduction of new modifications so that by 1 April 1968, the F-105 system manager was working 34 different modification programs involving approximately 639,000 manhours. For example, on 31 March 1968, the Air Force approved modification of 65 F-105Ds to receive an improved visual bombing capability, a more precise navigation system, and a better blind bombing capability (Loran D). This modification was dubbed Thunderstick II, and it included the reinforcement of fuselage stations and the installation of a saddleback to house the avionics equipment.

Testing was, however, hindered by numerous problems. The AN/ARN-85 Loran system proved difficult as well as expensive, to maintain. These problems lasted until September 1969, when the prototype Thunderstick II aircraft was successfully flight tested with the AN/ARN-92. The result was that after all only 30 F-105Ds were converted to Thunderstick II aircraft. The final F-105 selected for "T-stick II" modifications was completed in July 1971 and reached McConnell AFB on 4 August for service with the 563rd Tactical Fighter Squadron. However, not a single T-stick Thud ever saw combat action.

Meanwhile, as the war in Southeast Asia ground along, the danger from improved SA-2s increased as the enemy received newer and more sophisticated systems from their Soviet and Chinese suppliers. Accordingly, the Air Force worked to improve its anti-SAM capabilities, resulting in yet another Thunderchief model: the F-105G. This version featured improved Fansong signal detection capability and a better weapons delivery system, the inclusion of the ALQ-105 in two blisters alongside the fuselage, and a dual AGM-45 Shrike capability. Originally, 51 Thuds were modified, but at a later date twelve more F-l05Fs were upgraded as well. The F-l05Gs saw action in Southeast Asia from 1970 through the end of the conflict.

The F-105s (more than 800 were eventually produced) fill a proud page in the history of Air Force operations. Thuds and Thud drivers carried the brunt of the war during Operation Rolling Thunder. General William W. Momyer’s tribute was, like the aircraft, blunt and to the point: "The F-105 Thunderchief with its outstanding speed and ruggedness permitted us to carry the war to the heart of the enemy. Its speed at low altitudes made it the finest aircraft in the war."

Utrecht, Netherlands
and
Sumter, South Carolina

Note

1. Marcelle Size Knaack, Encyclopedia of US Air Force Aircraft and Missile Systems: Volume I, Post-World War II Fighters (Washington, D.C.: Office of Air Force History. 1978)

Editor’s note: Some of the photographs used in this article were provided by the International Agency for Aviation Photographs.

The authors are working on a book about the F-105 in Southeast Asia. They would appreciate stories, anecdotes, and photographs from air and ground crews that served with Thunderchief units there. The addresses are:

P.O. Box 9194
3506 GD Utrecht
Netherlands
2282 Ginko Dr.
Sumpter, SC 29150

Contributor

Theodore W. van Geffen, Jr. (A. A., Zeist Junior College, Netherlands) in Assistant Manager, Institute of Systematic Botany, State University of Utrecht, Netherlands; a free-lance aviation journalist, focusing on the F-105 Thunderchief; and a photographer for the Japanese aviation magazine Aviation Journal. He was the first aviation journalist to visit and photgraph the Egyptain Air Force after the Camp David Peace Treaty.

Senior Master Sergeant Gerald C. Arruda is a production supervisor, RF-4C aircraft, 363rd Tactical Fighter Wing, Shaw AFB, South Carolina. He has served as Superintendent of the F-105 Maintenance Engineering Section, Hq TAC, and was an F-105 crew chief in Southeast Asia. Sergenat Arruda is a graduate of the Tactical Air Command NCO Academy and USAF Senior NCO Academy.

Disclaimer

The conclusions and opinions expressed in this document are those of the author cultivated in the freedom of expression, academic environment of Air University. They do not reflect the official position of the U.S. Government, Department of Defense, the United States Air Force or the Air University.


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