At the Dawn of the Jet Age, the F-84 Thunderjet was a Rumbling Presence
Designed by Republic Aviation Corporation engineer Alex Kartveli — progenitor of the P-47 Thunderbolt — the F-84 Thunderjet became the US Air Force’s second operational jet fighter but the first to enter service after World War 2. Overshadowed by the debonair F-86 Sabre during the Korean War and dubbed The Hog in tribute to their sluggish take off behaviour, F-84s provided diligent service as ground attack jets, possessing superior range, speed and survivability to the F-51D Mustang and F-80C Shooting Star. Thunderjets and the successor swept wing F-84F Thunderstreaks were the prevalent aircraft in Strategic Air Command’s little known strategic fighter squadrons, as well as the air forces of America’s European allies who urgently needed to rearm for the Cold War. Since the F-84 was in service when jet technology had just passed its infancy, it was a test subject for a variety of quirky, sometimes fatal aerial experiments.
The F-84 almost did not achieve production status. When the then P-84 (its classification before 1948) made its first test flight in 1946, Republic was nearing bankruptcy. The wartime success of the P-47 Thunderbolt notwithstanding, the company only had enough money to function for three weeks. Reprieve for the nascent jet was achieved when the US Army Air Force agreed to advance payment on the aircraft eight months ahead of delivery, along with a handy $6 million tax refund from the government.
Contrary to the toughness displayed by the P-47 and later Republic produced aircraft, the early versions of the Thunderjet were quite fragile. The production F-84B, of which 226 were produced, introduced an ejection seat which was not reliable enough to be cleared for practical usage. Its fixed armament of 4x 0.50 calibre M3 machine guns in front of the canopy and one per wing root would arm all succeeding Thunderjet models and the F-84F Thunderstreak. 191 F-84Cs followed on with underwing stores for 1000 lb bombs and improved fuel, electrical and hydraulic systems, but still failed to achieve safety certifications for the ejection seat. Just 154 D models were produced with the J35-A-15 engine adding 1000 lb more thrust to the B and C models; it was also the first Thunderjet type to see combat in Korea. It was quickly discovered that the Thunderjet would run out of runway space, especially in summer.
According to Thunderjet pilot Jim Simpson, early models were ‘really lousy’; fuselage and tail sections were mash ups of mismatched serial numbers from cannibalization and there was no confidence in the ejection seat or emergency systems which were safety wired as ‘closed’. The absence of a Bendix fuel control could stall the jet if excessive fuel was fed to the engine by pushing too much throttle. The US Navy did find a job for several F-84Bs though — as F-84KX target practice drones.
When the North Korean People’s Army (KPA) invaded South Korea in June 1950, F-82G Twin Mustangs, F-51D Mustangs and F-80C Shooting Stars carried out most of the US Air Force’s tactical operations against communist formations. Thunderjets only started arriving in the Korean warzone in December 1950, two months after Chinese intervention on North Korea’s side. They were duly put to work as escorts for B-29 Superfortress bombers which were pounding the communist armies and North Korea’s rudimentary industrial base. At this early stage of its Korean deployment, the majority of Thunderjets were F-84Es, featuring a lengthened fuselage and canopy — appreciated by pilots for the roomier cockpit and luggage room behind the (now functional) ejection seat for personal gear. Just as important was an AN/APG-30 radar ranging gun sight for accuracy and mounting brackets for Jet Assisted Take Off (JATO) booster bottles to get The Hog off the runway.
Unfortunately, the Thunderjet was a lacklustre bomber escort against the swept wing MiG-15bis jet fighter. While the F-84E possessed the range to accompany Superfortresses over North Korean territory, its Soviet built adversary was speedier at 670 mph (the F-84E’s top speed was 620mph), more manoeuvrable and outclassed the Thunderjet at higher altitudes (51000 ft ceiling vs 43240 ft). The F-84 was rapidly relieved in the escort and air superiority mission by the F-86A Sabre, which was the Americans’ only available equivalent to the MiG.
Where the F-84 found its forte was razing troops, convoys, power plants and even dams with bombs, napalm, rockets and gunfire volleys while surviving long enough to escape retaliation compared to its peers. The World War 2 vintage F-51D Mustang delivered ordnance with more precision owing to its slower speed and could take off from shorter airfields than jets — an invaluable ability at the war’s beginning when the only South Korean territory in UN hands was the shrinking Pusan perimeter. Conversely the Mustang’s virtue of lower speed and inline engine made it more fragile to air defences. The Thunderjet outshone its jet companion, the F-80C Shooting Star in speed (620 mph vs 580 mph) and operational range (1485 miles vs 1090 miles). In contrast to its earlier models, the F-84E and G (appearing in Korea in 1952) could absorb more punishment than either the Mustang or Shooting Star and was appreciated as a stable gun platform. Last of the straight wing Thunderjets, the G model was also the most prolific model at 3025 being manufactured compared to 843 F-84Es. Aside from a J35-A-29 engine boasting 5600 lbs thrust, an autopilot and a framed canopy resembling the wartime Japanese A6M Zero’s, it was the first US jet fighter with air to air refuelling capability and the means to deliver Mk 7 tactical nuclear bombs. While the F-84G did not make use of its nuclear strike capability in battle, being able to refuel from KB-29 tankers was invaluable when flying from bases in Japan. Thunderjets were credited with destroying 60% of communist ground targets claimed by the USAF and flew 86408 sorties in the conflict.
The Next Evolutionary Step: Thunderstreak and Thunderflash
Back in the US, Republic was working on a ‘YF-96A’ fighter by adding swept wings and vertical stabilizers to an F-84E fuselage; with a top speed of 693 mph, it was faster than either the original F-84E or F-86A Sabre. The Air Force’s early disinterest quickly gave way to a contract after its tussles with the MiG-15 in Korea. The resulting F-84F Thunderstreak endured a tortured development process rivalling its Thunderjet forbears: it necessitated a tail redesign and reinforced wings because test models ripped off the latter if they stalled upwards; the fuselage had to be deepened and intake enlarged to accommodate the Wright J65 engine. An American import of the British Sapphire engine mounted in the Gloster Javelin, almost four versions were successively fitted to the F-84F owing to its chronic unreliability. While the Thunderstreak first flew in 1951, these problems delayed its entry into operational service until 1954.
By far the longest lived variant of the Thunderjet family — in overseas, rather than American service — was the RF-84F Thunderflash. Built to replace the small quantity of RF-80A/C Shooting Stars and RF-86A/F Sabres in the USAF inventory, this derivative of the F-84F necessitated a complete redesign of the nose by moving away the engine intake to enlarged wing roots and stuffing 6 cameras into what was now a cone shaped construct. Aside from the blunt nose section, RF-84Fs could be distinguished from their F-84F parents by fences on their wing surfaces to mitigate stalling. Early RF-84Fs mounted four M3 machine guns in their wing roots but these weapons were deleted as production progressed.
While the Average Joe would associate Strategic Air Command (SAC) as the agency for operating nuclear capable bombers and ballistic missiles, most variants of the Thunderjet family served in its short lived and forgotten fighter wings. Contrary to Tactical Air Command (TAC) which operated fighters for air superiority, battlefield interdiction and close air support, SAC fighter wings were originally intended as bomber escorts and airfield defence. The debut of the mid air refuelling capable F-84G and the advent of smaller nuclear bombs to go with them expanded these formations’ duties to strategic strike support. While nuclear bombers such as the B-36 were designated for attacks on Soviet population and industrial centres if World War 3 broke out, SAC fighters would set out to eliminate their nuclear delivery platforms to mitigate the number of doomsday warheads heading towards the US mainland. Following a dismal six month tenure with the fragile F-84B in 1948, successive variants of E and G model Thunderjets and F-84F Thunderstreaks served in SAC’s fighter wings from 1949 until their dissolution and handover to TAC in 1957.
Making an Export Thunderclap in Europe and Beyond
Although the members of the F-84 family did not serve for a particularly long period in US service because of more advanced aircraft like the North American F-100 Super Sabre and McDonell F-101A Voodoo displacing them, the Hog enjoyed a bountiful acceptance through MDAP (Mutual Defence Aid Programs) in Western Europe, whose nations lacked the means to produce their own aircraft while their industries were lying in rubble after World War 2. The Thunderjet’s export proliferation was also assisted by the misfortunes of the only friendly European country with a functioning aviation industry. (The other was the then hostile Soviet Union, which was arming its Eastern European and Asian clients). Britain seemed set to dominate the military aviation market with the Gloster Meteor and de Havilland Vampire and indeed, sold several to Denmark, Belgium, the Netherlands and elsewhere.
The reality of the Meteor and Vampire was that they were designed during the war and were already outdated by the time they entered service. The next wave of British aircraft like the Hawker Hunter were delayed by government imposed vetoes on using existing centrifugal engines until more advanced axial flows were available. Consequently, F-84G Thunderjets took over the fighter bomber inventories of France, Holland, Belgium, Denmark and Italy while the F-86 Sabre dominated the air superiority fighter market. Although the F-84F Thunderstreak and RF-84F Thunderflash were hobbled by their engine reliability problems, they outnumbered the Hawker Hunter considerably and were distinguished as West Germany’s first jet fighters when they resurrected the Luftwaffe. When these countries updated their inventories with aircraft from their rebuilt industries or with the next generation of bestselling imports like the F-104 Starfighter, Greece and Turkey inherited F-84s of all types, extending their service lives into the 1990s. Further to the east, Iran, Thailand and Taiwan operated F-84Gs until the mid 1960s while Yugoslavia (a communist nation) used them until the 1970s.
Exotic and Dangerous Experiments
The need to prepare for a possible war with the Soviet bloc coinciding with mankind trying to understand the possibilities and limits of jet technology made for an age of sometimes quixotic experiments with the F-84 as a guinea pig. Many of these tests resulted in wrecked jets and lives lost.
If World War 3 occurred, long range bombers like the gigantic Convair B-36 and B-29 Superfortress (now downgraded to a medium bomber) would need to penetrate Soviet airspace which would certainly be defended by interceptors. While the bombers had multiple crew members who could take turns resting on their intercontinental journeys, single pilot escort fighters did not have such a luxury.
TIP TOW attempted to circumvent the problem by clamping a specially modified EF-84D to each wingtip of an ETB-29A mothership. The EF-84D’s wingtips mounted lances which fitted into retractable, rubber sealed sockets on the carrier ship’s own wing tips. In theory, the attached fighters could save on fuel by turning off their engines. While the first phase of experiments in October 1950 passed without incident, the tethered fighter pilots had to manually compensate for vibrations resulting from the carrier ship’s wingtip vortices by moving their elevators, negating the aim of reducing crew fatigue over long flights.
A second round of TIP TOW experiments with automatic flight control in April 1953 ended violently when an EF-84D flipped over into its host bomber’s wing. Both aircraft crashed into Peconic Bay, eastern Long Island, without survivors. TIP TOW’s failure did not deter the Air Force from making another attempt at the wingtip docking idea. In September 1956, the sequel project TOM TOM was abruptly dumped when an RF-84F was forcefully ripped from the host RB-36F’s wing.
FICON (Fighter Conveyance) continued with the concept of parasite craft, this time to perform nuclear strikes or reconnaissance rather than as escorts. FICON dispensed with TIP TOW’s wing tip attachments for an extendable arm folding out from the host GRB-36F bomber’s bomb bay. 25 RF-84F Thunderflashes with skyhooks and lowered tailplanes — dubbed RF-84Ks — served for a year in trials without TIP TOW’s tragedies but the slowness of attaching to the host ship in adverse weather, retirement of the B-36 and advent of the Lockheed U-2 spyplane in 1956 sealed the program’s demise.
As airfields have always been priority targets in wartime, experiments in vertical/short take off and landing (V/STOL) concepts were all the rage, with an EF-84E modified for ZELMAL (Zero Length Launch, Mat Landing) trials. The fantastical idea involved blasting an F-84 mounting a scaled up JATO booster off a TEL (Transporter Erector Launcher) normally used for B61 Matador cruise missiles. Once the fighter had performed its mission, it would land by plonking itself onto an inflatable mat. While the launch trials starting in December 1953 encountered no faults, the first mat landing experiment six months later proved a spine breaking flop. Aside from the Thunderjet’s arrestor hook ripping a gash in the mat, the impact shattered the aircraft beyond repair and inflicted severe back injuries on its test pilot.
An alternative take on STOL aircraft was the mating of an F-84F with a turboprop engine, counter-torque fin behind the canopy and modified T-shaped tail plane to keep the horizontal stabilizers out of the propeller’s backwash. Two airframes of the resulting XF-84H were tested by the Air Force after the US Navy dropped out of the program. Only a dozen test flights were conducted from 1955–56 before the program’s termination. Even if the aircraft’s shabby handling and frequent gearbox failures could tolerated, the propeller’s savage noise output was capable of inducing vomiting symptoms in a large radius, earning the unofficial title of ‘Thunderscreech’.