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The Republic F-105 Thunderchief

v2.0.7 / 01 nov 2016 / greg goebel

* The Republic "F-105 Thunderchief" was conceived in the 1950s as a nuclear strike aircraft, but would achieve fame in the Vietnam War as the "Thud", a conventional strike and "defense suppression" aircraft. This document provides a history and description of the F-105.

Republic F-105D Thunderchief


[1] F-105 ORIGINS
[2] F-105B IN SERVICE / F-105D / F-105F
[3] THUNDERCHIEF OVER VIETNAM
[4] THE COUNTERMEASURES WAR
[5] WILD WEASEL
[6] NORTHSCOPE / T-STICK II / COMBAT MARTIN
[7] TWILIGHT
[8] COMMENTS, SOURCES, & REVISION HISTORY

[1] F-105 ORIGINS

* In 1951, a design team under Alexander Kartveli at Republic Aircraft began work as a company venture on a new high-performance, single-seat low-level nuclear strike aircraft. The new aircraft, which was given the company designation of "Advanced Project 63 (AP-63)", was to replace the Air Force's Republic F-84F Thunderstreak.

Many different design concepts were considered, gradually evolving towards something along the lines of a "stretched" F-84F with a bombbay for a nuclear weapon. The aircraft was to be powered by an Allison J71 turbojet, though as it turned out this powerplant would not have enough thrust for the aircraft that finally flew and was never actually used. The AP-63 would also be able to carry air-to-surface missiles (ASMs) and air-to-air missiles (AAMs) on underwing pylons. It was to have a top speed of Mach 1.5, and would be capable of defending itself against enemy fighters. The aircraft would have sophisticated combat avionics and mid-air refueling capability.

Initial contracts were awarded to Republic in 1952 and 1953 for what at first was a total of 199 aircraft, with initial delivery scheduled for 1955. In reality, USAF requirements were shifting at the time, even to the point of shutting down the project for a short time at the end of 1953, and the company did not receive a solid contract until February 1955, for 15 aircraft. These 15 aircraft were finally completed as two "YF-105A" evaluation aircraft; three "RF-105B" reconnaissance aircraft; and ten initial production "F-105Bs".

* The initial flight of the first YF-105A was on 22 October 1955, with Republic test pilot "Rusty" Roth at the controls. The second prototype followed on 28 January 1956. The YF-105A was a sleek, big aircraft with mid-mounted wings swept back 45 degrees; similar sweptback tail surfaces, with an "all moving" tailplane; engine intakes in the wing roots; a ventral fin for yaw stability at high speeds; and tall, stalky tricycle landing gear with single wheels. The main gear hinged in the wings, retracting towards the fuselage, and the nose gear retracted forwards.

The wings were relatively small for the aircraft's size to gave it high "wing loading" that ensured a smoother ride at low level -- though at the expense of agility, and with the price of a long take-off run. Flight controls were hydraulically boosted. The pilot sat in a cockpit with a clamshell canopy, on a Republic-designed rocket-boosted ejection seat.

Although the plan was to fit production aircraft with the Pratt & Whitney (P&W) J75 turbojet, since the J75 was not available at the outset the two YF-105As were powered by the P&W J57-P-25 turbojet, with 45.4 kN (4,625 kgp / 10,200 lbf) dry thrust and 66.7 kN (6,800 kgp / 15,000 lbf) afterburning thrust. Despite the fact that the J57 was substantially less powerful than the J75, the YF-105A was still capable of Mach 1.2.

Republic YF-105A

* Both YF-105As were forced to make wheels-up landings in March 1956, with both breaking their backs but the pilots walking away; the two machines were written off. Fortunately, the first F-105B was delivered in mid-May. It performed its initial flight on 26 May 1956, fitted with the P&W YJ75-P-3 engine with 71.2 kN (7,260 kgp / 16,000 lbf) dry thrust and 105 kN (10,660 kgp / 23,500 lbf) afterburning thrust. The F-105B-1 also differed from the YF-105As in having reverse-swept instead of forward-swept air intakes, plus an "area-ruled" fuselage:

The initial F-105B suffered damage during its first flight when its landing gear failed to extend, due circumstances resulting in a suction effect that kept the gear doors closed. The pilot had to belly in, which he did with considerable skill; when he walked away from the plane, the gear doors popped open. The machine was back in the air in six weeks.

* In addition to the accidents, the development effort was also complicated by the fact that USAF requirements were continuing to shift, but these changing requirements also led the USAF to become more enthusiastic about the "Thunderchief", as it was formally named in June 1956. In March 1956, the service had ordered 65 more F-105Bs and 17 RF-105Bs, followed by an order for five two-seat "F-105C" trainers to provide instruction in the Thunderchief's advanced avionics systems.

The RF-105B was canceled in July 1956, though as mentioned three prototypes, lacking armament and photographic gear, were completed. They were used in special trials under the designation of "JF-105B". The F-105Cs were axed in 1957, but F-105B production went ahead. The other nine F-105B initial production machines were completed, with the first five being "Block 1" or "F-105B-1" aircraft and the rest being "F-105B-5" aircraft. First flight of a production aircraft, an "F-105B-6", was on 14 May 1958.

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 KPH (1,216 MPH) over a 100-kilometer closed course in an F-105B.

* While Republic was getting the F-105 into the air, the company was also considering designs for a high-speed long-range interceptor for a 1954 USAF requirement. The Republic submission to the Air Force, the "AP-75", was clearly similar to the F-105 but featured twin side-by-side engines and swept triangular flight surface; it was to be armed with AAMs carried in an internal weapons bay. The USAF selected the North American F-108 Rapier for the competition; however, that is another story.

BACK_TO_TOP

[2] F-105B IN SERVICE / F-105D / F-105F

* The Thunderchief was a complicated aircraft, leading to high maintenance hours. The electronic systems were particularly unreliable, the hydraulic systems badly needed redundancy, and the airframe needed reinforcement. Initially, the aircraft required 150 maintenance hours per flight hour to keep it in the air, and so aircraft availability rates were poor. However, efforts to work out the bugs continued, and in time Republic and the Air Force began to get ahead on the serviceability curve, with F-105Bs brought up to snuff through a program designated Project OPTIMIZE.

When the Thunderchief was in flying condition, it was an impressive aircraft, like its Republic ancestors big, rugged, and powerful, but unlike them sleek and photogenic. The sweptback wings featured low-speed ailerons and high-speed spoilers to improve handling, as well as full-span leading-edge flaps to improve take-off and landing characteristics. The Thunderchief also featured an interesting airbrake system consisting of four "cloverleaf" segments around the jet exhaust that opened like flower petals. The cloverleaf airbrake also served as a variable engine exhaust, opening nine degrees automatically when afterburner was engaged. Only the horizontal petals could be extended when the aircraft's landing gear was down, to keep the bottom petal from striking the runway.

Full production F-105Bs were powered by a P&W J75-P-19 engine, with 71.6 kN (7,300 kgp / 16,100 lbf) dry thrust and 109 kN (11,100 kgp / 24,500 lbf) afterburning thrust. The aircraft was fitted with a single General Electric (GE) M61 six-barrel 20-millimeter Vulcan Gatling-type cannon, firing from the left side of the nose. The fighter could also carry 3,630 kilograms (8,000 pounds) of stores in its bombbay, as well as an additional total of 1,815 kilograms (4,000 pounds) of stores on five external stores pylons, with one pylon on the aircraft centerline and two under each wing.

Weapons targeting was performed by an "MA-8" fire control system (FCS), with an AN/APG-31 ranging radar, K-19 gunsight, and a "toss-bombing" system to allow the aircraft to release a nuclear munition in a climb and turn away from the blast. Incidentally, the unproduced RF-105B reconnaissance variant didn't have the Vulcan cannon and the FCS, these being replaced by a five-camera nose, but it was to be fitted with twin Colt M39A1 20-millimeter cannon, one under each engine intake, for self-defense.

The bombbay could accommodate a Mark 28 or Mark 43 nuclear weapon, though as the Thunderchief became more focused on conventional attack the bombbay was usually fitted with an auxiliary fuel tank with a capacity of 1,476 liters (390 US gallons). The internal fuel capacity without the bombbay tank was 4,396 liters (1,160 US gallons) in seven tanks in the fuselage. The F-105B could also carry two 1,705-liter (450 US gallon) drop tanks, one on each inboard stores pylon, and another 1,705-liter or 2,464-liter (650 US gallon) drop tank on the centerline pylon. Total fuel capacity could be as high as 11,750 liters (3,100 US gallons). The aircraft was fitted for probe-and-drogue inflight refueling, with a retractable probe on the left side of the nose just forward of the cockpit.

* Including the test and evaluation machines, only 75 F-105Bs were built in all, with the last six "F-105B-20" aircraft rolled out in late 1959. The F-105B equipped four USAF squadrons, with the variant phased out to the US Air National Guard (ANG) in 1964. Some of these aircraft were passed on to the Air Force Reserve later.

The F-105B was followed by improved variants. The USAF had already requested modifications to the F-105B for all-weather operation in November 1957, well before the Thunderchief entered service, leading to the definitive "F-105D". The F-105D's nose was stretched by 38 centimeters (1 foot 3 inches) to accommodate the "AN/ASG-9 Thunderstick" FCS, vastly superior to the F-105B's MA-8 FCS. The AN/ASG-9 featured the "R-14 North American Search And Ranging Radar (NASARR)", a multi-mode radar that provided air-to-air, air-to-ground, and low-level terrain-following capability; and the GE "FC-5" automatic flight-control system, which provided navigation and weapons-delivery capabilities. Cockpit instrumentation was updated accordingly. The circular dials of the F-105B's cockpit were also replaced with horizontal and vertical "tape" style indicators that were much easier to read.

The F-105D was powered by an uprated J75-P-19W turbojet with water-methanol injection, providing 118 kN (12,000 kgp / 26,500 lbf) maximum thrust. Intake ducting was modified to provide more airflow, while the airframe, landing gear, and brakes were strengthened to handle the increased weight. The F-105D also incorporated an arresting hook at the rear of the ventral fin to snag runway cables on an overshoot.


   REPUBLIC F-105D THUNDERCHIEF:
   _____________________   _________________   _______________________
 
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                10.59 meters        34 feet 9 inches
   wing area               35.77 sq_meters     385 sq_feet
   length                  19.61 meters        64 feet 4 inches
   height                  5.97 meters         19 feet 7 inches

   empty weight            12,475 kilograms    27,500 pounds
   max loaded weight       23,970 kilograms    52,840 pounds

   max speed at altitude   2,240 KPH           1,390 MPH / 1,210 KT
   service ceiling         13,720 meters       45,000 feet
   range with tanks        3,850 kilometers    2,390 MI / 2,080 NMI
   _____________________   _________________   _______________________

The armament and weapon load was the same as the F-105B, but the entire 5,450-kilogram (12,000-pound) weapon load could now be carried externally. The F-105D could also carry four "Sidewinder" AAMs or four "Bullpup" ASMs.

Initial flight of the first of three "F-105D-1s" was on 9 June 1959, with deliveries to TAC beginning in early 1961. However, late in 1961 all F-105Ds were grounded when an airframe failed a fatigue test in the laboratory. The problem was quickly corrected.

353 more F-105Ds were produced in a series of minor block changes up to the definitive "F-105D-25" production block, of which 80 were built. All earlier production was brought up to F-105D-25 specification through an update program designated "Project Look-Alike", begun in 1962 and completed in 1964. In addition, 39 "F-105D-30s" were built with improved instrumentation, and then 135 "F-105D-31s" with dual probe-and-drogue / boom refueling capability, adding a tanker boom socket in the nose. Total F-105D production came to 610 machines, with the last delivered in 1964.

Republic F-105D, F-105F

* Although in 1959 the Air Force had canceled a second proposed two-seat version of the F-105 -- a combat-capable derivative of the F-105D, designated the "F-105E" -- once the Thunderchief was in service the USAF found that a two-seater F-105 was a real necessity, since coming up to speed on the type was not trivial. The Air Force ordered yet another two-seat version, the "F-105F". The first flew on 11 July 1963, with Republic test pilot Carl Arderey at the controls, with the type going into USAF service at the end of the year.

The F-105F featured tandem clamshell canopies, in contrast to the single canopy intended for the earlier two-seater concepts; dual flight controls; the dual inflight refueling capability of the F-105D-31; a taller tailfin; and a fuselage stretch of 79 centimeters (31 inches) to accommodate the second cockpit. The F-105F was fully combat-capable, even retaining the Vulcan cannon, and could deliver nuclear munitions. The decision to give the two-seater combat capability would prove far-sighted.

The last of 143 F-105Fs was delivered in January 1965, ending Thunderchief production. The word had come down from the top to concentrate on the McDonnell F-4 Phantom for the attack role. The final production tally was:

   YF-105A:     2
   RF-105B:     3
   F-105B:     75
   F-105D:    610
   F-105F:    143
   ______________

   TOTAL:     833

All F-105s went into service with the USAF. No other US service operated the Thunderchief, and the type was never exported.

BACK_TO_TOP

[3] THUNDERCHIEF OVER VIETNAM

* Just as Thunderchief production was coming to an end, America's war in Southeast Asia was ramping up. The USAF 36th Tactical Fighter Squadron (TFS) relocated from Japan to Korat Air Force Base in Thailand in August 1964. These F-105s were supposed to be used to provide cover for air rescue operations, but in practice they were often used as strike support for US Central Intelligence Agency operations in Laos. On 14 August 1964, Lieutenant Dave Graben's F-105D was chewed up by flak over Laos. Graben made it back to Korat and landed safely, but his aircraft had to be written off. It was the first Thunderchief to be lost to enemy action.

Six months after the introduction of the Thunderchief to Southeast Asia, the 36th TFS was relocated to another base in Thailand at Takhli, about 160 kilometers (100 miles) to the northwest. The 35th TFS moved into Korat. More Thunderchief units arrived, eventually constituting the 6234th Tactical Fighter Wing (TFW) at Korat and the 6235th TFW at Takhli. Some F-105 squadrons were operated from the Da Nang air base in South Vietnam for a short period of time early in the war, but they were then relocated to Thailand.

The US government denied that the Air Force was operating out of Thailand until 1966, but in fact the F-105s were very busy. They conducted a month-long bombing campaign designated BARREL ROLL beginning in early December 1964. BARREL ROLL was intended to support Royal Laotian forces fighting with the North Vietnamese Army and Communist Pathet Lao insurgents.

That was just a warm-up to a bigger air war. On 7 February 1965, in response to an attack by Communist Viet Cong guerrillas against a US base camp in South Vietnam, American President Lyndon Johnson ordered Operation FLAMING DART to strike targets in North Vietnam. The strikes were conducted by US Navy, US Air Force, and South Vietnamese Air Force aircraft, with the F-105s making their initial sorties into North Vietnam itself on 8 February. The Viet Cong responded with further raids on American facilities in South Vietnam, and the US responded with more air attacks.

Matters escalated into a prolonged air campaign against North Vietnam codenamed ROLLING THUNDER, with the first attack performed on 2 March 1965. ROLLING THUNDER was largely the brainchild of US Defense Secretary Robert S. McNamara, and had the objective of pressuring North Vietnam to the bargaining table by performing a series of restrained but increasingly severe strikes, hence the codename. The 2 March strike didn't give much reason for confidence in the scheme: three F-105s and two F-100 escorts were shot down, with four pilots killed and one becoming a prisoner of war (POW). The North Vietnamese seemed barely disturbed by the attack. Indeed, as the losses showed, they had been expecting it.

* The F-105 became the USAF's primary strike aircraft for ROLLING THUNDER, ironically because the Air Force was reluctant to risk the loss of their B-52s, the backbone of their strategic bomber force. In a further irony, B-52s were heavily used for tactical strikes, particularly on the Ho Chi Minh Trail.

The F-105 took the brunt of the early air war. Pilots were generally fond of the big, sturdy, powerful machine, giving it names such as "Lead Sled"; "Super Hog"; "Ultra Hog"; "Iron Butterfly"; and most of all "Thud". That was at least originally the sound it was supposed to make when it crashed into the jungle, since it got off to a bad start in combat, but Republic engineers worked overtime to fix some of the machine's lingering defects. The lack of hydraulic redundancy would never be completely overcome, but soon the name "Thud" was used as a measure of respect for the aircraft's blunt-instrument sturdiness and brutal effectiveness. The F-105D could take a lot of punishment and come back home. In 1966, one F-105 was hit with a flak round that took out a chunk out of its wing 1.2 meters (4 feet) across, and the aircraft still limped back to base.

The major complaint against the F-105 was that it was, like all its Republic ancestors, a real "Earth lover" that always needed as much runway as it could get to make it into the air. Jokers liked to say that if a runway was built that circled the Earth, Republic would still be able to build an aircraft that used it all. The F-105's highly loaded wings did give it an unbeatable fast ride at low altitude, but they didn't give the Thud much in way of maneuverability, the thing being generally regarded as about as agile as a brick.

The F-105 could be fitted with multiple ejector racks on its centerline to carry six bombs, along with a MERs on the inboard pylons to carry four per pylon. The outboard pylon could not be fitted with a MER. Fully loaded up, the Thud could carry sixteen 340-kilogram (750 pound) bombs, giving it an impressive strike capability. It could carry other air-to-ground munitions, such as napalm canisters and 70 millimeter (2.75 inch) unguided rocket pods. It could also carry four AIM-9 Sidewinder AAMs using a special rack allowing two to be carried on a single stores pylon. Since the bombbay wasn't used on these strikes, it was normally fitted with an auxiliary internal fuel tank. The natural metal finish sported by F-105s up to that time gave way to a more warlike camouflage scheme, with a disruptive pattern of tan, green, and olive drab on top, and white on the bottom.

North Vietnam was divided up by the US military into a set of target zones referred to as "Route Packages (RPs)" -- the name being derived from the packets of maps and data issued to flight crews for each target zone. As the air attacks ramped up, so did the effectiveness of North Vietnamese air defenses, and US losses continued to rise. The most heavily defended area was "RP-6A", in and around Hanoi. US pilots referred to Hanoi as "downtown", a reference to the contemporary Petula Clark pop hit of the same name, whose lyrics included the line: "Everything's waiting for you there." To enter into this target area, the F-105s had to fly over a high natural wall that became known as "Thud Ridge".

The missions were dangerous and losses were high. At the worst of the air war, the chances of a Thud pilot surviving 100 missions over North Vietnam were about 75%. To increase frustration of the pilots, the air war was being "micromanaged" from the top by President Johnson and Defense Secretary McNamara. The strikes were conducted with highly specific "rules of engagement (ROEs)" that defined what was to be hit and what wasn't.

ROEs are now common in the limited warfare that has become the style in the post-Cold War world, but they were more or less a new idea in 1965 -- one that Air Force pilots had not been trained for, and that the politicians in charge didn't have a clear handle on. The ROEs seemed to shift frequently with no understandable rhyme or reason. What was absolutely clear to Thud pilots, however, was that they were getting shot at by a fearsome air-defense network, and their squadron mates weren't always coming back.

BACK_TO_TOP

[4] THE COUNTERMEASURES WAR

* The North Vietnamese air defense system consisted of three layers of weapons:

The network was supported by a number of wide-area surveillance radars to track intruders. Not all the gear in the network was entirely modern, but it was still very effective overall, and something had to be done about it. At first, "strike packages" were often led by a Douglas EB-66 Destroyer electronic countermeasures (ECM) aircraft to jam air-defense radars. The EB-66 was slow, however, and it wasn't a satisfactory solution.

* The obvious solution in hindsight was to give the F-105s their own defensive ECM systems, but the process proved difficult. General Electric had already developed a "Quick Reaction Capability 160 (QRC-160)" underwing jammer pod for fighter aircraft, with initial tests in 1962 and a batch of 150 "QRC-160-1" pods delivered for service in 1963. They were stockpiled and ignored; ECM wasn't part of the fighter culture, and fighter jocks simply saw the pods as clutter that cut into performance.

Now there was a need for the pods, and in the summer of 1965 a set of pods was yanked from storage in Okinawa and sent to South Vietnam. They were operationally tested on McDonnell RF-101 Voodoo reconnaissance aircraft and proved ineffective -- for the simple reason that, having been left derelict for a few years, they were almost all broken. Nobody had tried to test them, largely because they neither knew how nor had any test gear. After some ineffectual fumbling, the effort was given up.

However, back in the US, Lieutenant Colonel Ingwald "Inky" Haugen, an electronic warfare specialist at Eglin AFB in Florida, was working on how to make better use of the QRC-160-1 pod. It was a "noise jammer", meaning it simply threw out static on the frequency band of the adversary radar -- as opposed to a "deception jammer", which played tricks with the radar return signal to confuse the radar. By itself, a single pod wasn't much good against the SA-2 SAM. Instead of a nice clear dot on the radarscope, the jammer would produce a big fuzzy blur. A SAM could be launched against the center of the blur, and the SAM's proximity fuze would detonate the big warhead when it got close enough, resulting in a "kill".

Haugen had suggested a few years earlier that bombers carrying noise jammers could fly in groups of four, separated by few hundred meters horizontally and a smaller distance vertically. This would produce a nice big blur on the radar scope where nobody could figure out where the targets were, like hunting for bugs under a blanket. Since US bombers penetrating Soviet airspace could expect to get a SAM with a nuclear warhead that would take them all out anyway, Haugen's idea didn't fly at the time. However, North Vietnamese SA-2s weren't fitted with use nuclear warheads -- Soviet aid to North Vietnam would not include nukes -- and so the idea now seemed much more practical.

Initial tests were performed under the codename PROBLEM CHILD at Eglin in October 1965, with four F-105s carrying two jammers to deal with a substitute for a Fan Song radar. It seemed to work well, and then the pods were modified by GE engineers to exploit specific features of the Fan Song, making them extremely effective. The modified pods were designated "QRC-160A-1".

By the end of 1965, Eglin was pushing use of the pods in Southeast Asia, only to be told: "Get lost." Eglin hadn't heard about the fiasco with the pods in South Vietnam, and the completely negative attitude came as a surprise. Eglin didn't give up, however, and pushed for a proper demonstration of the pods. The combat squadrons had their hands full at the time and didn't want to bother, even though pilots were literally being slaughtered, but the word came down in September 1966 that a new evaluation would be performed. Flights of four Thuds, carrying pods set to the frequency bands of the Fan Song and Fire Can radars, were sent on combat missions. The North Vietnamese almost completely ignored them, preferring to expend resources on strike aircraft that they could see and hit.

It didn't take long for the attitude of the combat squadrons to change completely. By early October they were demanding the pod, which in full production would become the AN/ALQ-72. There weren't enough to go around at first, but operational tests showed that an F-105 only needed to carry one, as long as there were enough aircraft in the package hauling them to provide overall band coverage. By November 1966, all Thuds going into combat would carry a pod, and new and more effective pods, including pods with both noise and deception jamming capabilities, would be introduced on a steady basis. Aircraft crews approaching defended territory would run their last system checks and switch on their ECM gear, getting green lights on their cockpit panels to show that things were working. The slogan was: "Clean up, green up, and turn on the music."

Of course, with everyone carrying pods, the North Vietnamese could no longer ignore flights carrying jammers to focus on those that didn't. Everyone got their fair share of SAMs and AAA, but the trade was worthwhile: the North Vietnamese now had to fire five times as many SA-2s to score a kill. The EB-66s no longer escorted strike packages, instead being used for "stand-off" jamming of long-range surveillance radars.

BACK_TO_TOP

[5] WILD WEASEL

* Jamming amounted to a passive response to the threat posed by North Vietnamese air defenses; the Air Force also chose a more active response, launching strikes against the air-defense sites. The first attempt at an "Iron Hand" defense-suppression mission took place on 27 July 1965, and it was a complete disaster. The Thuds attacked SAM sites that had been located by air reconnaissance, only to run into heavy AAA. Six F-105s were lost, including two to a mid-air collision that killed both pilots, and an RF-101 Voodoo went down as well.

They did hit the SAM sites, but post-strike reconnaissance indicated the sites were dummies, with wooden missiles and other props. The North Vietnamese were expecting the SAM sites to be hit and not only set up dummy sites, but switched real batteries around over a set of pre-prepared sites on a continuous basis. The sites were always well camouflaged and heavily protected by AAA. Following Iron Hand missions didn't do much better, with a dismal report issued in mid-September concluding simply: "Results have been negative." The Americans were thrashing around in the brush, getting hit over the head with a brick by a tricky enemy who could see them coming. The Americans needed to reconsider their game plan.

* Back in the US, an electronics firm named Applied Technology INC (ATI), out of Palo Alto, California, had been working on countermeasures gear. ATI generally worked on secret "black" programs and built specialized equipment in small lots. One of their projects had been the "System XII" lightweight radar warning receiver (RWR) for the Lockheed U-2 spyplane. System XII was far in advance to every other RWR in existence at the time, and in response to USAF feedback, ATI had developed a derivative named "Vector" with the Boeing B-52 bomber in mind.

Vector could pick up radar signals over a wide band and display the threats on a little round 7.6-centimeter (3-inch) display. A strobe from the center of the display would point in the direction of the threat radar, with the length of the strobe giving the intensity of the radar signal, with a dotted, dashed, or solid line giving the frequency band of the radar.

When the SAM threat in Southeast Asia raised its ugly head, USAF officials working with ATI arranged a demonstration of the Vector for the top brass, who were suitably impressed. ATI also began to push the company's "IR-133" panoramic scanning "radar homing and warning system (RHAWS)", a more elaborate state-of-the-art gadget that could provide precise targeting of adversary radars. The Air Force snapped them up, immediately ordering that Vector and IR-133 gear be installed in two-seat North American F-100F Super Sabre fighters. An "electronics warfare officer (EWO)" in the back seat would control the systems, with the Vector gear used to detect active air-defense sites, and the precision IRC-133 RHAWS used to pinpoint it so it could be bombed straight to hell. The codename for the project would become famous: Wild Weasel.

The four Wild Weasel F-100Fs were in service in Southeast Asia at the end of November 1965. ATI had come up with a third electronic box for the aircraft in the meantime, the "WR-300" launch warning receiver (LWR), which picked up the radio command signal that kept an SA-2 SAM on course. If the WR-300 picked up such a signal, it meant that a missile had been launched.

The Wild Weasel was something new, and it took time to get results. As mentioned, the SAM sites were carefully camouflaged, hard to find even with ATI's magic black boxes, which were also of course entirely new gear and so not highly trustworthy. A Weasel was lost on 20 December 1965, the pilot being killed and the EWO taken prisoner. The Weasels finally scored on 22 December, with one EWO saying the Vector scope lit up like a "Christmas tree" from radar contacts. They pounded the site with unguided rockets and cannon fire until it was a flaming ruin. The Weasels went back home without losses and a sense of deep satisfaction: after six months of being kicked around, the Iron Hand was making itself felt.

* The F-100F had proven the Wild Weasel concept, but it couldn't keep up with F-105 strike packages, and it was withdrawn from service in January 1966 after having served its purpose. The logical thing to do was to use F-105Fs instead, and the first of 86 Wild Weasel conversions were in combat by May 1966. They featured the Vector RWR, IR-133 RHAWS, WR-300 LWR, and a fourth box, the "SEESAM". A Fan Song radar produced two fan-shaped radar beams, wide but thin, one vertical and one horizontal. When a beam locked on to the target, the rate of radar pulses increased abruptly to provide tracking; when both beams locked on to a target, it was in the "crosshairs" and a SAM launch was imminent. SEESAM would turn on an indicator light when a Fan Song lock occurred. The light was labeled the "AS" for "Azimuth Sector", but pilots called it the "Aw Shit!" light instead.

The Weasel F-100F crews hadn't really been in action long enough to learn the game very well, and the Weasel F-105F crews went through their own nasty learning curve. By the summer of 1966 they were having brutal confrontations with SAM sites. Wild Weasel F-105Fs often worked with F-105Ds in "hunter-killer" teams, with the Wild Weasel Thud pinpointing the target and the F-105Ds destroying it.

The Iron Hand F-105Fs and F-105Ds were armed not only rockets, iron bombs, and cluster bombs, but with the new "AGM-45 Shrike Anti-Radar Missile (ARM)" -- a modified Sparrow AAM with a radar-seeking head, which had been put into action by the Weasel F-100Fs late in their short service career. The Shrike would home in on an active radar, but it had a number of limitations: it needed to be fitted with a specific head for a specific type of radar, meaning one configured to hit a Fan Song radar wouldn't see a Fire Can radar; its range was much shorter than that of an SA-2; and it would lose target lock if the enemy turned off the radar.

Later on the Weasels would carry the big AGM-78A "Standard Anti-Radar Missile (STARM)", an air-launched variant of the US Navy's "Standard" SAM with a radar-seeking head. It was so hefty that it required use of a reinforced stores pylon. It had to be fitted with a specific head as well, but it had a lot more stand-off range, a bigger warhead, and a seeker with a memory system that allowed it to maintain its target track even if the radar was turned off.

* The enemy, always shrewd, learned to be ever more conservative in the use of radar to avoid being picked up by the Weasels, but that was all for the good: if the radars weren't transmitting, they weren't targeting American aircraft. The Weasel crews became increasing shrewd themselves at their job, popping up over a hill to get a fix on a radar site, popping back down again, and then arcing around a hill to hit the site from an unexpected angle. Those who survived the harsh learning curve began to feel confident in their ability to find and take on enemy air-defense sites.

That didn't mean it was always easy. While other aircraft avoided air-defense sites when possible, Wild Weasels actually had to attract their attention and take them on. This led to the Wild Weasel motto of "YGBSM", standing for "You Gotta Be Shittin' Me!" -- this being the reaction of the first Wild Weasel aircrews when they were told what they were getting themselves into. The back-seater EWOs had particular reason to feel they had been thrown off into the deep end. They were pulled in from B-52 crews, bombers having long carried suites of defensive countermeasures, and the mindsets there were relatively staid. One of the EWOs commented: "We had never seen a fighter pilot up close before. They were trained to be aggressive and obnoxious, and they didn't disappoint us."

Two Wild Weasel F-105F pilots won the highest American military award, the Congressional Medal of Honor (CMH). On 10 March 1967, Captain Merlyn F. Dethlefsen was piloting one of two Wild Weasel F-105Fs, accompanied by two F-105Ds, that were paving the way for a strike package. It turned out to be one literal hell of a mission.

The leader of the flight was almost immediately shot down by AAA, with both aircrew captured. The AAA also hit an F-105D, forcing it to go back home. Each of the surviving Thuds was carrying two Shrikes; they fired all four without effect. They came out of the target area after expending the Shrikes, only to run into two North Vietnamese MiG-21 interceptors. They were easy to shake, sort of: the North Vietnamese followed Soviet air-defense doctrine, and one of its features was that interceptors and ground defense sites rigidly operated in their own zones. If an interceptor went into a ground defense site zone, it would be fired on without hesitation, no questions asked. The two F-105s went back into the target area and the MiGs didn't follow. The Thuds came through the flak bursts and out the other side, only to find two more MiG-21s. Dethlefsen and his wingmate turned back in again.

Dethlefsen's back-seater, Mike Gilroy, later commented: "Merle was a hard-headed Dutchman, once he grabbed hold of something he wouldn't let go. We were not there to suppress the defenses, we were there to kill them. The flak was terrible, as bad as I had ever seen." The two Thuds made one pass on the site but fumbled it; they came around again, Gilroy got a lock, said: "OK, that's it!" -- and the two Thunderchiefs pounded the target with iron bombs and cluster munitions. Both F-105s got back home, low on fuel and much the worse for wear. Dethlefsen was personally awarded the CMH by President Johnson. Gilroy got the Air Force Cross.

Not long afterward, on 19 April 1967, Lieutenant Colonel Leo K. Thorsness had completed an Iron Hand strike when his wingmates were shot down. He was low on fuel but stayed around to cover the air rescue operation, driving off a flight of MiG-17s that tried to interfere. Thorsness shot down one MiG and damaged another. He passed up an opportunity to refuel from a tanker when another aircraft breathing fumes showed up, and landed safely at Ubon, a forward base in Thailand. On 30 April, Thorsness' F-105 was hit and badly damaged. He and his EWO ejected, Thorsness being badly injured in the process, and were captured by the North Vietnamese. They spent over six years in a North Vietnamese POW camp.

* The Air Force was so enthusiastic about ATI's magic boxes that the service ordered the Vector and WR-300 into mass production as the "AN/APR-25" and the "AN/APR-26" respectively, to be put on all strike aircraft. The boxes began to go into combat service on F-105Ds in November 1966, about the same time as the jammer pods went into action, with the installation revealed by an antenna fairing under the nose and a small antenna on the top rear of the tailfin. Simply being notified of a missile launch and its direction was a great help. A pilot could dodge the SAM fairly easily if he knew it was coming, turning toward it and then veering off at the last moment. The SA-2 hadn't been designed with agility in mind, and it would not be able to turn quickly enough to bring the fighter into the blast radius of its warhead.

Republic F-105G Wild Weasel

The Wild Weasels got their own updates in turn. 56 Wild Weasel F-105Fs were updated to an improved Wild Weasel configuration with the designation "F-105G". They carried improved magic boxes, including an AN/APR-35 RWR, an AN/APR-36 LWR, and an AN/ALR-31 RHAWS. After initial flights, they were also fitted with a distinctive built-in jamming system, the AN/ALQ-105, which was an AN/ALQ-101 countermeasures pod that had been split in half and faired into the sides of the belly. This was done so that the F-105G wouldn't have to use up a stores pylon to carry a jammer pod. Finally, they could carry the improved AGM-78B-1 STARM, which had a two-band radar seeker head, and then the AGM-78B-2 STARM with an "all-band" head.

The Wild Weasels were one of the great air adventure stories of the Vietnam War. Late in the conflict, an Air Force assessment team did a rigorous analysis of the effectiveness of USAF electronic warfare systems in the combat theater and gave the Weasels high marks. Ironically, the assessment concluded that Shrikes only hit a radar antenna about 5% of the time, and that the rate of actually finding and destroying enemy SAM sites was low. The true value of the Weasels was in sheer intimidation: when the Weasels were around, SAM launch rates dropped by 90%, allowing strike packages to reach their targets without interference.

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[6] NORTHSCOPE / T-STICK II / COMBAT MARTIN

* There were a few other F-105 modifications that saw relatively little use. In early 1967, a number of F-105Fs were given a night-strike capability, with a modified R-14A radar system for improved targeting and other, minor, changes for night operations. These were known as "Northscope" or "Commando Nail" aircraft. It appears that the updated radar system still lacked the accuracy to be useful for tactical strike; using the radar meant maintaining a straight and level course, making the aircraft a relatively easy target, and Commando Nail was abandoned after about a year.

* In late 1967, about a dozen F-105Fs serving in Vietnam were fitted with a Hallicrafters AN/QRC-128 VHF radio jammer to disrupt communications between MiG pilots and their ground controllers. Another feature of Soviet air-defense doctrine was that interceptor pilots were under rigid ground control, being allowed very little initiative. That meant cutting the ground control link would seriously disrupt interceptor operations.

Jamming a radar took relatively low power, since it was a matter of interfering with the faint return echo from a radar pulse. In contrast, jamming communications meant disrupting a direct link from a transmitter to a receiver, and so it took substantially more power to drown out a voice link with raw noise. The AN/QRC-128 took a trickster's approach to the matter, recording the voice conversation and then playing it back after a momentary delay, resulting in a garble that was very difficult to understand.

The big box, called "Colonel Computer" by flight crews, replaced the back-seat crew member. These aircraft were referred to as "Combat Martins" and were identifiable from a large square blade antenna just behind the cockpit. They could carry a full warload and, since the AN/QRC-128 didn't need to be closely monitored, could deliver ordnance along with the rest of the strike package.

Combat Martin F-105F

The US National Security Agency (NSA), which controls US strategic signals intelligence and was monitoring North Vietnamese communications, learned about the program, and ordered it stopped. The NSA's attitude was that the intelligence obtained by listening in on the fighter controller channels outweighed the benefits of jamming. Since this was the NSA's domain, their word was law, and all the effort and expense involved in the program went down the drain; it is unclear if the Combat Martins flew a single operational mission. Beginning in 1970, the Combat Martins were converted to the F-105G Wild Weasel configuration.

* In 1969, 30 F-105Ds were fitted with advanced attack avionics under the "AN/ARN-92 Thunderstick (T-Stick) II" program, featuring an AN/ARN-92 LORAN radio-beacon navigation system receiver to permit precision strikes at night or in bad weather. The LORAN avionics were stored in a fat dorsal fairing that ran from cockpit to tail. However, by this time the F-105D was being withdrawn from combat; the T-Stick II aircraft never went to war, serving out their time stateside.

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[7] TWILIGHT

* By the spring of 1968, the ROLLING THUNDER campaign had proven a clear failure. American losses had been high and the North Vietnamese proved entirely indifferent to the attempt to bomb them by gradual increments to the negotiating table. A month-long bombing halt was called, somehow appropriately, on 1 April 1968, with intermittent strikes dwindling away until they stopped completely on 1 October. They were formally called off on 1 November, since American presidential elections were coming up.

There were no more strikes to the north for about three years. During this time, the F-105s were withdrawn from the strike role, the survivors going back home. The last strike mission of the F-105 was on 6 October 1970. However, Wild Weasel Thuds remained on hand for combat. Attacks on North Vietnam in earnest in the spring of 1972, beginning with an operation codenamed FREEDOM TRAIN, intensifying into LINEBACKER I, to finally end with a climax of destruction named LINEBACKER II during the Christmas season that year. The bombing was far less restrained and much more effective than before, with LINEBACKER II finally pushing the North Vietnamese to the bargaining table.

Wild Weasel Thuds were in the thick of the action, generally operating in hunter-killer teams with Phantoms to make the most of the limited numbers of F-105Fs still available for combat. They stayed in action until the US finally ended its overt involvement in the war in early 1973.

* The loss record of the Thunderchief in the war speaks volumes about the level of its commitment. 395 F-105s were lost, with only 61 of these losses due to operational accidents. AAA and SAMs were the worst hazard, taking down 312 F-105s; AAA was much more dangerous than SAMs, performing the lion's share of these kills. North Vietnamese MiGs claimed 22 Thunderchiefs, but the Thuds more than evened the score, with the F-105 credited with the destruction of 27.5 MiGs; interestingly, 24.5 of these kills were performed with cannon alone. This is very much the opposite of the kill records of the other major fighter types in the war, the Vought F-8 Crusader and the F-4 Phantom, in which most kills were achieved with AAMs.

Thunderchiefs began to be transferred from USAF service to the Air Force Reserve and ANG in January 1971, with the last Thunderchiefs, F-105Gs, in USAF service sent to the Reserves in July 1980. The last flight of a Reserve Thunderchief, an F-105D, was on 25 February 1984, and the Thud was out of service with the ANG in early 1985. There are many survivors on static display, but none remain in flying condition.

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[8] COMMENTS, SOURCES, & REVISION HISTORY

* The F-105B actually was the mount for the USAF "Thunderbirds" flight demonstration team for a short time in the spring of 1964. These aircraft featured special modifications, including replacement of the Vulcan cannon with ballast, a few reinforcements for aerobatics, and addition of a smoke generator. However, after flying a few displays, on 9 May 1964 one of the F-105Bs broke in half and exploded after the team flew low over the runway to do a "pitch-up" and come around for a landing; the pilot, Captain Gene Devlin, was killed. F-105Bs were grounded until a structural reinforcement program had been implemented. The Air Force reconsidered use of the F-105B as an airshow performer, and the Thunderbirds went back to the F-100 Super Sabre.

Republic F-105D Thunderchief

* One of the popular stories concerning the Thud was the "airstrike" four F-105s made on the USAF Academy in Colorado Springs. In June 1968, an F-105 was being dedicated as a static display at the Academy. The cadet commandant, famous fighter pilot Robin Olds, was in charge of the ceremony and the cadets were lined up to witness the event, which turned out to be more exciting than anyone anticipated.

Four Thuds performed an overflight as part of the ceremony, first roaring over in "fingertip-four" formation. They flew off in the distance and the cadets could see them wheeling around, in the F-105's usual wide circle, to perform a second high-speed overflight in file. However, as the first aircraft approached, the cadets had an instant to realize that they couldn't hear it, meaning it had broken Mach 1. The aircraft passed over, followed by a tremendous sonic boom and sound of the windows in the hall behind them shattering outward in shards of glass. The other Thuds in the file popped out their airbrakes and tried to climb to avoid adding to the damage.

The cadets found all this exciting; reports of Olds' reaction range from "amused" to "enraged". It sounds like a yarn, but pictures survive of the vast expanses of broken glass, a boarded-up window carrying a cardboard sign with AIR CONDITIONING BY REPUBLIC scribbled on it. Most recollections insist that the pilot wasn't disciplined; the F-105s had come from Kansas and he had failed to factor in the "mile-high" ground level at the Academy, in the shadows of the Rockies, which made the speed of sound lower.

* I only saw a working F-105 once. I was rotating out of the US Army in late August 1975 and was in out-processing at Fort Dix, New Jersey. With time on my hands and nothing better to do, I was wandering around and went out the main gate. There was an air base right next door and I got treated to an unforgettable view of a monster aircraft throttling up to pour fire and sound out its exhaust as it prepared for take-off.

* As concerns copyrights and permissions for this document, all illustrations and images credited to me are public domain. I reserve all rights to my writings. However, if anyone does want to make use of my writings, just contact me, and we can chat about it. I'm lenient in giving permissions, usually on the basis of being properly credited.

* Sources include:

Some details were also obtained from a very thorough web document by aviation enthusiast Joe Baugher.

* Revision history:

   v1.0.0 / 01 sep 01 
   v1.0.1 / 01 jan 02 / Minor bug fixes, review & polish.
   v1.0.2 / 01 jan 03 / Minor bug fixes, review & polish.
   v2.0.0 / 01 jan 05 / Expanded discussion of electronic systems.
   v2.0.1 / 01 jan 07 / Review & polish.
   v2.0.2 / 01 apr 07 / Minor corrections.
   v2.0.3 / 01 mar 09 / Review & polish.
   v2.0.4 / 01 feb 11 / Review & polish.
   v2.0.5 / 01 jan 13 / Review & polish.
   v2.0.6 / 01 dec 14 / Review & polish.
   v2.0.7 / 01 nov 16 / Review & polish.
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