The American V-1 Program 1944-1950

Beginning in 1942, Allied intelligence began a systematic analysis of the Fiesler Fi 103 flying bomb better known as the V-1. Analysis of crashed test articles combined with photoreconnaissance and intelligence collected by agents within occupied Europe led the United States in particular to restart its flying bomb programs in 1943 that had laid dormant for the most of the Second World War on account of what was felt to be beyond the current state of the art. In 1944, Northrop was contracted to begin development of the first US flying bomb, designated the JB-1. Running parallel to the Northrop effort was the reverse-engineering of the V-1 using 2,500 lbs of salvaged V-1 parts that had been provided by Great Britain. The parts arrived at Wright-Patterson Field in Dayton, Ohio, on 13 July 1944 and the US Army Air Forces directed the engineering staff there to build 13 copies of the V-1. Quite remarkably, the USAAF technical staff completed the first copy in just three weeks! To put the scope of the success of the Allied intelligence effort and the work the Wright-Patterson Field team into perspective, the first German V-1s struck Britain on 12-13 June 1944. By the end of the following month, the USAAF had its first copy of the V-1 and they had test fired the reverse-engineered pulse jet engine. A memo from the technical team responsible to General Henry Arnold, head of the USAAF, recommended mass production at the earliest opportunity- however, General Arnold and his advisors were well aware of the V-1's inaccuracy and despite reservations that production of an American V-1 would divert crucial wartime resources and manpower from battle-proven weapons, it was felt that if the guidance of the V-1 could be improved, an American version might be useful. 

The Republic-Ford JB-2 differed from the V-1 in minor details
(USAF/Wikipedia)

Republic Aviation was tasked with producing the American V-1 which was designated JB-2 with the first of the thirteen USAAF copies arriving on 8 September 1944 from Wright-Patterson Field. The USAAF ordered 1,000 JB-2s from Republic. The Ford Motor Company was tasked with producing the JB-2's pulse jet engine which was designated the PJ31. With Republic's resources nearly all committed to the production of the P-47 Thunderbolt, the company subcontracted the airframe assembly to Willys-Overland, the same company that built the Jeep. With Ford responsible for engine production, the Jack & Heintz Company of Cleveland which had been building aircraft electrical components and autopilots as a subcontractor was given responsibility for the JB-2's control system. Alloy Products of Wisconsin was given responsibility for the fuel tanks and pressure vessels used in the JB-2 while the Northrop was contracted for the JB-2's launch sled. The booster rockets that actually propelled the JB-2 off the ground were contracted to Monsanto. 

By the end of September 1944, the USAAF revised its initial order for 1,000 JB-2s to 1,000 JB-2s *per* month with a target goal to reach that rate by April 1945. The first JB-2 launch took place at Eglin Airfield in Florida on 12 October 1944- just three months had elapsed since start of the German V-1 campaign against London and the first American copy had made its first flight! Flight testing was also carried out at Wendover Field in Utah at the same time that the B-29 Superfortress unit that dropped the atomic bombs, the 509th Composite Group, was a tenant at Wendover training for their special mission. The flight tests didn't go too smoothy- by the first week of December, there were two successful flights out of ten launches. 

JB-2 air launch from a B-17 at Eglin Army Air Field in 1944
(USAF/Wikipedia)

Northrop's own flying bomb design, the JB-1, made its first launch in December 1944 but crashed after launch. (The JB-1 will be the subject of its own later article here at Tails Through Time.) With the the early failures of the JB-1 and problems with its jet powerplant, the USAAF decided to continue with the development of the Northrop design but production and operational priority went to the JB-2. Despite issues with accuracy in the flight tests at Eglin and Wendover, the USAAF leadership pushed for an increased production rate for the JB-2 to at least 3,000 per month. On 14 January 1945, General Arnold ordered another 75,000 JB-2s with the ability to launch 100 per day by September and 500 per day by January 1946 in anticipate of the invasion of Japan. On the next day, the JB-2 program got the same priority that was given to the B-29 Superfortress program. 

Despite the enthusiasm from the USAAF leadership, theater and operational commanders were skeptical of the JB-2. The generally poor European weather that was interfering with the strategic bombing campaign, however, offered perhaps some utility for the JB-2 as it wasn't dependent on clear weather- a view supported by Sir Trafford Leigh-Mallory, the head of the Royal Air Force and commander-in-chief of Allied air forces for the Normandy invasion as well as General Carl Spaatz, head of US Strategic Air Forces Europe. Spaatz, however, was a bit more measured in his support for the employment of the JB-2. He felt that it was more a harassment weapon that could be used when bad weather precluded a strategic bombing mission and outlined his planned use at 300 JB-2s per day only 10 days out of the month. But General Spaatz was very specific that operational employment of the JB-2 could not interfere with heavy bomber operations and he personally expressed concerns to General Arnold regarding the JB-2's cost-effectiveness given its inaccuracy. 

The JB-2 flight test program centered primarily on improving the weapon's accuracy. The first successful flights in the fall of 1944 showed an average error of eight miles at a range of just over 120 miles, not much better than what the Germans were averaging in their own V-1 campaign. The next step by the USAAF was to install radio guidance control in the JB-2. Using a radar beacon and remote control, it was thought the JB-2's accuracy could be improved. However, continued flight tests showed in 20 flight tests with the new guidance system, the JB-2's average error was no better than it was before with preset controls. Things did get better though- by war's end, the JB-2 with preset controls was averaging 5 miles error over a range of 150 miles and 1/4 mile error over a range of 100 miles with radio guidance. 

The biggest stumbling block to the operational deployment of the JB-2 in Europe in 1945, believe it or not, was logistical. The sheer numbers of JB-2s needed competed with other munitions production and it was estimated by some in the War Department that just transporting the JB-2 and its associated equipment to Europe would take up nearly 25% of Allied shipping capacity in the Atlantic. Brief consideration was given to moving JB-2 production to Europe, but there simply wasn't the production capacity anywhere else but the United States to produce the numbers of JB-2s planners envisioned using. 

With the end of the war in Europe, JB-2 production numbers remained in flux as planners debated what was needed for the planned invasion of Japan. By this point, however, the production and logistical concerns for the mass deployment of the JB-2 had exhausted the initial enthusiasm for the weapon. Production was halted initially at the end of January 1945 but then reinstated at a lower rate. By the time of the Japanese surrender, 1,385 JB-2s had been built when production was terminated.

Concurrent with the USAAF testing, the US Navy worked on a navalized version of the JB-2 that would have been launched from specially-modified LSTs and escort carriers during the invasion of Japan. Fifty-one JB-2s were requested by the Navy for its own testing program in September 1944 when production was launched. While airborne launches from B-17 Flying Fortresses were done during testing at Eglin Field, the Navy planned to launch JB-2s from Consolidated PB4Y Privateers as well. Navy planners, however, didn't expect operational capability with the JB-2 (which was called the Loon by the Navy) until August or September 1946. The first Navy Loon launch was on 7 January 1946 with the Secretary of the Navy approving the conversion of two submarines for Loon operations in March 1946. Conversion of the USS Cusk (SS-348) began in January 1947. The Cusk entered the history books on 18 February 1947 as the world's first missile submarine when it made its first Loon launch...which ended in failure after only 3.5 miles of flight. The Cusk finally had its first successful launch on 7 March 1947 after five tries. Submarine launch had become the Navy's focus for the Loon program with the USS Carbonero (SS-337) also modified for the program and by 1949 finally carried out a firing from a surface ship, the test ship USS Norton Sound. In March 1950, the Navy terminated in the Loon in favor of the more promising Regulus cruise missile. 

The USS Cusk fires a JB-2 Loon
(US Navy/Wikipedia)

With the US Air Force becoming independent in 1947, the JB-2 program was reactivated in March 1948 at Holloman AFB in New Mexico as part of a program for the development of missile guidance systems and seeker technology. Work using the JB-2 benefitted the later Matador cruise missile program with the JB-2 program winding down by 1949 with test airframes successfully being flown remotely and skid landed for recovery. A joint effort with Eglin AFB also used the JB-2 as a target drone for the development of gunsights. Interestingly "Flakzielgerät 76" was the German cover name for the V-1 during its development which loosely translates as anti-aircraft target device.

Further reading:

British Defenses Against the Summer 1944 V-1 Bombardment
Regulus: The US Navy's First Operational Nuclear Missile
CHECK SIX: Ships Damaged or Sunk by the Yokosuka MXY7 Ohka

Sources: The Evolution of the Cruise Missile: Comprehensive History from the V-1 and V-2 to the Tomahawk and Snark by Kenneth P. Werrell. Air University Press/USAF, 1983, pp 79-85. V-1 Flying Bomb 1942-1952: Hitler's Infamous Doodlebug (New Vanguard No. 106) by Steven J. Zaloga. Osprey Publishing, 2005, pp 39-41.

Major Merlyn Dethlefsen and the Medal of Honor Wild Weasel Mission of Lincoln 03

Major Merlyn H. Dethlefsen

By March 1967, Operation Rolling Thunder had been going on for two years with no signs of North Vietnam backing down. The United States and North Vietnam engaged in a gradual escalation of the conflict. As US air strikes increased, the Hanoi regime increased its anti-air defenses from AAA to the more deadly SA-2 surface-to-air missiles as well as MiG fighters. The skies over North Vietnam would be the most dangerous and difficult skies for American pilots to operate in since World War 2. At the start of Rolling Thunder, defense suppression was assigned to two-seat F-100F Super Sabres known as the Wild Weasels. The F-100 was in interim solution for the Wild Weasel role, though, as it had a limited payload and wasn't fast enough to keep up with the F-105 Thunderchiefs that were shouldering the burden of strike missions at the time for the USAF. In June 1966 the first Thunderchief Wild Weasels arrived in Southeast Asia. One of the Wild Weasel units at the time was the 354th Tactical Fighter Squadron at Royal Thai Air Force Base (RTAFB) Takhli which was home to the F-105s of the 355th Tactical Fighter Wing. The 355th TFW had been operating the Thunderchief since 1962 at McConnell AFB in Kansas before being deployed for Rolling Thunder. Like the F-100Fs, the Wild Weasel F-105Fs had two crew, the pilot and the electronic warfare officer in the back, the EWO or "Bear". 

Dethlefsen and Gilroy in their Wild Weasel F-105F

On 10 March 1967, the target portfolio was finally expanded to include the large Thai Nguyen steel works. The area was the center of North Vietnam's heavy industry and the only steel mill (it actually was the first steel mill in Indochina, having started production in 1959) and for most of the first two years of Operation Rolling Thunder, it remained off the target list for political reasons. A large Thunderchief strike package made up of single-seat F-105Ds and Wild Weasel F-105Fs for defense suppression was sortied against the steelworks by the 355th TFW from RTAFB Takhli. One flight of four Wild Weasels with the call sign "Lincoln" was part of this strike package on this day. As the flight approached Thai Nguyen, Lincoln Lead's Bear locked up a SAM site and an AGM-45 Shrike missile was fired, but it missed. The SAM site, however, did not, and in short order Lincoln Lead along with two F-4 Phantoms flying escort were shot down. Lincoln 02 took flak damage and had to withdraw and limp back to Takhli. That left only two Wild Weasels in the area, Lincoln 03 piloted by Major Merlyn Dethlefsen and his Bear, Captain Kevin Gilroy, and their wingman, Major Ken Bell in Lincoln 04. As Dethlefsen and Gilroy targeted the SAM site, two VNAF MiG-21s entered the fight, closing in on Dethlefsen from behind. Lincoln 03 fired their Shrike missile and immediately hauled the heavily laden F-105F into a hard turn, causing the missiles from the attacking MiG-21s to go wide and miss. Gambling that the MiGs wouldn't follow him into the flak zone that protected the SAM site, Dethlefsen pressed on instead of jettisoning his bombs as was the practice when jumped by MiGs- for the VNAF, getting a Thunderchief to jettison its bombload was as good as shooting it down since it wouldn't be able to press its attack. Sure enough, the MiGs didn't follow him to the deck and at low altitude, Dethlefsen hit the afterburner to regain altitude. Just as he had reached position to hit the SAM site, another pair of MiGs closed in and opened fire on Lincoln 03 and Lincoln 04. Both took 37mm cannon hits but were still flying. 

With the last of the strike F-105Ds and their Phantom escorts egressing the area, Dethlefsen knew the weather forecast was good for the next several days and that the Thai Nguyen steel plant was long on the wish list for the pilots to hit. Though he would have been in his right by USAF procedure to follow the rest of the aircraft and leave the area for Takhli, Dethlefsen elected to take another crack at the SAM site as he knew more of his fellow pilots would be returning over the next several days. Leading his wingman, Dethlefsen scanned the flak pattern from a safe altitude while Kevin Gilroy acting as his Bear got a bead on the SAM site with the Wild Weasel's electronics. Once Gilroy pinpointed the site, they fired their Shrike missile to knock out the guidance radar. Dethlefsen then led his wingman down into the flak zone to put the SAM site out of business. Getting a visual on the site, Dethlefsen unleashed his bomb load across the site and then pulled out. For added insurance, he rolled his damaged Thud into a reverse flip, switched to guns and hosed the site down with his 20mm Vulcan cannon. He then nursed his F-105F out of the target zone and hooked up with a KC-135A tanker on the way back to Takhli. 

Merlyn Dethlefsen and his EWO, Kevin Gilroy

It was a Medal of Honor performance, but what did Dethlefsen do that was so brave? First of all, by USAF procedure he was to have exited the area as the strike package left- one of the mottos of the Wild Weasels was "First in, last out". Instead, he decided to take another crack at a SAM site. Dethlefsen wasn't naive. On the day of this mission he already had 72 Wild Weasel combat missions under his belt. He knew if the site wasn't knocked out, it would more than likely shoot down more crews in the coming days. And this wasn't just any target- this was a prized asset of the North Vietnamese and it was heavily defended. More American aircraft were shot down in 1967 than any other year of the Vietnam War. The skies over Thai Nguyen were not a good place to be for an American pilot that day, month, and year. Add to that the Wild Weasel mission profile that exposed their crews to hostile fire longer than most pilots. 

Merlyn Dethlefsen was born in 1934 on a farm in Iowa and he joined the USAF in 1954 through the Aviation Cadet Program. From 1957 to 1959 he served as a navigator on the Douglas C-124 Globemaster II out of Dover AFB before reporting to undergraduate flight training. His first operational assignment after getting his wings was flying F-100 Super Sabres in Germany before transitioning to the F-105 Thunderchief in 1965. After his Medal of Honor mission (his Bear, Kevin Gilroy, earned the Air Force Cross for that mission), he went on to complete his 100 mission tour in Vietnam. He would later go on to serve as an operations director for the SR-71 wing at Beale AFB in California and for the B-52 wing at Dyess AFB in Texas. Dethlefsen flew west in 1987 and was laid to rest at Arlington National Cemetery. 

Source: Above and Beyond: The Aviation Medals of Honor by Barrett Tillman. Smithsonian Institution Press, 2002, pp 225-227. F-105 Thunderchief Units of the Vietnam War by Peter Davies. Osprey Publishing, 2012. Photos: USAF Museum, Wikipedia.

Operational Improvisation: Over-the-Shoulder Nuclear Bombing

F-84Gs of the 20th FBW had lightning markings, each squadron had its own color

In 1952 the Republic F-84Gs of the 20th Fighter-Bomber Wing crossed the Atlantic supported by aerial refueling to set up shop at their new base, RAF Wethersfield, in order to provide tactical nuclear strike capability for the first time to NATO forces in Europe. Just a year earlier, scientists and engineers at Sandia, one of the development centers in the United States for nuclear weapons, had developed the Mark 7 nuclear bomb, the first tactical nuclear weapon with an explosive yield of 20 kilotons. While the Mark 7 weapon would be carried operationally by many USAF and US Navy tactical attack aircraft, the first aircraft to carry the Mark 7 operationally also happened to be the first production tactical fighter to have not just nuclear capability, but also air-refueling capability. That was specifically the G variant of the Republic F-84 Thunderjet, which had an air refueling receptacle for a flying boom in the left wing root, a more powerful jet engine, and provisions for the Mark 7's special pylon that had the necessary circuitry for nuclear weapons delivery. 

The Mark 7 was the first American tactical nuclear weapon

The 20th FBW had been given six months to prepare for the move to Great Britain as well as to become the first tactical nuclear fighter-bomber unit in military history. At the time of the deployment, the F-84Gs and pilots of the 20th FBW were only versed in clear-weather weapons delivery more suited to the bombing ranges in the predominantly sunny southwestern United States, drops being made starting at 20,000 feet in altitude. The weather in Europe, however, was far from ideal for this sort of weapons delivery mode, with a predominantly cloudy maritime climate in the areas that the 20th FBW was expected to operate. I had posted this past September about the nuclear delivery role assigned to the McDonnell F-101 Voodoos of the 81st Tactical Fighter Wing based in RAF Bentwaters/Woodbridge in the late-1950s and early 1960s. Not unlike the conditions facing the pilots several years later that flew the Voodoo, the pilots of the 20th FBW were expected to navigate visually and by dead reckoning to their targets with only the most basic of navigational aids. By the time the 20th FBW had set up shop at RAF Wethersfield, a different form of nuclear delivery was needed and the wing commander, Colonel John Dunning, had sent some of his best pilots to Kirtland AFB in Albuquerque, New Mexico near Sandia, to find out more about a new weapons delivery tactic called LABS- Low Altitude Bombing System. Developed at Kirtland by Major Jack Ryan, it hadn't yet received much attention as most nuclear delivery tactics of the day concerned use by strategic bombers. Col. Dunning wanted his pilots in Europe to have every advantage possible and LABS offered that prospect. 

In a LABS run, an IP (initial point) is chosen that is a known distance and direction from the target and was most ideally located three miles away. The LABS equipment was quite basic- it was a timer with a gyro that was free to move about the pitch axis of the delivery aircraft. Having previously set the time from the IP to the pull up point near the target and the calculated angle of release beforehand, an aircraft on a LABS run headed towards the target at 500 mph at low level with the IP in between the aircraft and the target. Once the IP was reached. the pilot pushed the "pickle" button on the control stick which started the timer and a flashing red light on the gunsight was connected to both the timer and the LABS gyro. The pilot pulled into a steady 4G climb and at a precise point and angle (usually 25 to 30 degrees), LABS released the nuclear weapon which continued onward on a precalculated ballistic trajectory towards the target while the pilot pulled his aircraft into an Immelman loop and exited the area as fast as possible. In effect, LABS "tossed" the bomb towards the target. 

Diagram showing the over-the-shoulder bomb toss

On return to Europe, the pilots that trained in the LABS technique for the 20th FBW found that finding an IP near the target was challenging. It was noted that as the distance between the IP and target decreased, the ideal release angle of the Mark 7 bomb increased. If the IP was very close to the target itself, then the optimum release angle was 90 degrees. Pushing the idea further, the pilots of the 20th FBW worked out that if the IP was the target itself, then the optimum LABS release angle was 110 degrees and the bomb would impact right at the point where the pull-up maneuver was initiated. No IP was needed- the target itself was the IP. The bomb was released "over the shoulder" and would arc upward to 10,000 feet and more than a minute elapsed before it detonated, allowing time for the F-84G to rollout and accelerate out of the area in a dive. The USAF and the specialists at Kirtland AFB doubted if the average USAF pilot could carry out such a complex maneuver as the wings had to be absolutely level in the pull up or the bomb's impact point would stray away from the target. The operations officer of one of the 20th FBW's constituent squadrons had noted that the F-84G didn't even need a LABS gyro- the aircraft's own gyro started to "tumble" right past vertical and by complete coincidence, right at 110 degrees! Major John J, Kropenick, the ops officer who made this observation, came up with his own solution, the "Kropenick Autopilot" that was taught to all the pilots of the 20th FBW- two large rubber bands were hooked to the control stick on the run in, each one then looped over a cockpit light on the sidewall on each side. The tension of the rubber bands kept the stick precisely centered during the pull up and once the Thunderjet's own gyro tumbled, the bomb would be released. Pilots taught the method with the "Kropenick Autopilot" had bomb scores acceptable to the USAF given the 20-kiloton yield of the Mark 7 bomb.

By the time the LABS equipment had been fitted to the 20th FBW's Thunderjets, the pilots of the wing had gotten quite proficient at using the "Kropenick Autopilot" and made the transition to using the LABS equipment for "over the shoulder" toss bombing with a minimum of delay and fuss. 

Source: Aviation History, March 2011, Volume 21, Number 4. "Over-the-Shoulder A-Bombing; Cold War F-84G pilots improvised a surprising twist on bomb delivery" by David Rust, p54-57.

Four years after its first flight the Republic F-105 Thunderchief in the form of the first production variant, the F-105B, finally reached operational status. Two years prior, though, planning had already begun for the definitive Thunderchief variant, the F-105D, and it was this variant that made up the bulk of the F-105's production run. The USAF's early plans were for 800 F-105s to equip 11 fighter wings of the Tactical Air Command. However, when the US Navy's new McDonnell F-4 Phantom II began smash existing records with its performance, Thunderchief production was abruptly curtailed in favor of the first USAF versions of the Phantom which offered a multirole versatility that the strike-optimized Thunderchief lacked.

Of the 833 Thunderchiefs built, 610 of them were F-105Ds and 143 were the two-seat F-105Fs that would later be converted into the F-105G Wild Weasel aircraft. All were built at Republic's Farmingdale, New York, facility on Long Island.

The Vietnam War, however, decimated the ranks of the F-105s. In the seven years that the F-105 flew combat missions in Vietnam from 1965 right into the 1972 Linebacker II attacks, of the 753 F-105D/F/G models that fought in the war, 395 of them were lost in the war- 296 of those losses were the single seat F-105Ds and the balance of that nearly 400 losses were the F-105F/G models. In addition to those staggering losses in the face of some of the most intense air defenses of the time, an additional 61 F-105s were lost in Southeast Asia from non-combat causes ranging from mechanical failures, engine problems, even mid-air collisions.

When the F-105Ds were withdrawn from combat in 1970, there were only enough Thunderchiefs for three USAF wings- the 347th TFW at Yokota AB in Japan, the 23rd TFW at McConnell AFB, and the 57th FWW at Nellis AFB. In less than two years, those F-105Ds were then passed on to Air National Guard squadrons (yes, squadrons- attrition left only enough Thunderchiefs at this point for single squadrons instead of entire wings) in New Jersey, Kansas, Virigina and the District of Columbia. Three USAF Reserve squadrons briefly operated the F-105D as well, but heavy combat use in Vietnam led to stress and fatigue in the Thunderchief's structure.

The Wild Weasel F-105Gs fared a bit better, having fought on to 1972 before US involvement in Vietnam ended in 1973. Enough of the G model Wild Weasels survived the war to equip three squadrons at George AFB in California where they served as trainers for crews destined for the more advanced McDonnell F-4G Phantom Wild Weasel. The survivors at George AFB ended up with the Georgia ANG.

With few Thunderchiefs left after Vietnam and many having used up their flight hours by the late 1970s, the F-105 had the dubious only of being the only US combat aircraft to be withdrawn from service solely on account of attrition rather than obsolescence.

Source: International Air Power Review, Volume 6, Autumn 2002. "Warplane Classic: The Republic F-105 Thunderchief" by Larry Davis, p120-155.

On his very first combat mission in 1915 flying a two-seat FBA flying boat to attack German gunboats, the young Alexander de Seversky would lose his right leg. After recuperation, he was assigned as the chief naval aircraft inspector for the Russian Imperial Navy's Petrograd district which gave him an appreciation for the design and production of aircraft. He worked closely with Dimitry Grigorivich on a series of flying boats that resulted in the M-9, the first Russian-designed naval aircraft to go into production during the First World War. Seversky encouraged Grigorivich to incorporate a machine gun mount as well as armor plating for the crew on the M-9.

Despite losing his flying status due to his injury, Seversky managed to perform an aerobatic display in the M-9 that enraged his superiors but won him the admiration of Czar Nicholas II, who ordered Seversky placed back on flying duty. Fitted with a wooden prosthesis and flying the plodding M-9 flying boat (it only had a maximum speed of 69 mph), he managed to score four kills against German aircraft. In 1917 he started flying a Nieuport 21 biplane and scored his fifth and sixth kills by single-handedly downing a German bomber and its fighter escort, bringing him to ace status.

In 1918 his status won him assignment to Washington D.C. as the Russian military attache with the embassy, but the Bolshevik Revolution that year resulted in him staying in the United States for good. He served as an assistant to Brigadier General Billy Mitchell in Mitchell's crusade to advance the cause for air power and Seversky would eventually establish his own aircraft manufacturing firm, Seversky Aviation, in Long Island, New York. In 1939 amidst a corporate reorganization Seversky was voted off the board by his own company which was renamed Republic Aviation. Another Russian emigre who worked for Seversky, Alexander Kartvelli, would take one of Seversky's designs, the P-35A fighter, and develop it further along a series of subsequent designs that culminated in the Republic P-47 Thunderbolt.

When he died in 1974, Seversky would hold 100 aviation-related patents and had received the Exceptional Service Medal for his advisory work for the U.S. Air Force in the 1960s.

Source: Aviation History, March 2010. "The Making of a War Hero" by James K. Libbey, p54-59.

Jet engine technology in the late 1940s was still immature enough that a jet-engined fighter often still lacked comparable range to a piston-engined fighter. As a result, both the USAF and US Navy saw the turboprop as the potential answer- the USAF hoped a turboprop fighter would offer a longer range and the US Navy was interested in the power of turboprop fighter to make takeoff from a carrier deck possible without a catapult. To evaluate the possibility, both branches agreed to fund an experimental turboprop fighter based on Republic's AP-46 design. The USAF would buy three and the US Navy would acquire a single example.

By 1951 the arrangement had changed to with only the USAF getting two AP-46 aircraft designated XF-84H. Although a development of the F-84F Thunderstreak, the XF-84H only had wing and canopy of the Thunderstreak with an all new fuselage and tail unit. A 5,580-horsepower Allison XT40 turboprop that drove via an 18-foot shaft a 12-foot three-bladed constant speed propeller. The Aeroproducts prop rotated at 3,000 rpm which meant that the blade tips traveled at Mach 1.18 and as such, created an immense amount of noise, leading to the XF-84H's name, the Thunderscreech. As the prop was constant speed, thrust was effected by adjusting the pitch of the prop.

With its first flight at Edwards AFB on 22 July 1954, it was immediately apparent the XF-84H had some serious flaws. Maximum deflection of the rudder was insufficient to counter the massive torque and p-factor of the supersonic prop. In addition, there were constant hydraulic problems, the elevator was limited in its pitch authority and the prop gearbox kept overheating.

But most famously, the XF-84H Thunderscreech was noisy. The supersonic prop blades were so loud that residents over 20 miles away from Edwards AFB filed noise complaints with the USAF! When the aircraft first taxied out under its own power and took off, the control tower crew often had to hide under their consoles shielding their ears. Any ground crew standing nearby often felt nausea and dizziness even with ear protection due to the Mach shockwaves from the prop blades.

As a result, Republic was banned from doing run ups on the flightline and it would have to be towed 7 miles away from the main ramp behind a ridge called "Rocket Hill" as it had rocket engine test stands in the area.

The second Thunderscreech arrived in May 1956 and was temporarily bailed to the US Navy in support of the VTOL tail sitting convoy fighter program as both the Lockheed XFV-1 and Convair XFY-1 used the same Allison XT40 turboprop engine. The last Thunderscreech flight was made on 9 October 1956 with cancellation following, much to the relief of the pilots, ground crew and most everyone at Edwards AFB!

Source: International Air Power Review, Volume 24 (Summer 2002). AIRtime Publishing, 2002. "Warplane Classic: Republic F-84, Thunderjet, Thundersteak, and Thunderflash" by David Willis, p124.