The Republic P-47 Thunderbolt

v1.2.0 / 01 jun 03 / greg goebel / public domain

* The Republic P-47 Thunderbolt was one of the main US Army Air Forces (USAAF) fighters of World War II. The P-47 was a big, rugged, overbuilt aircraft that was effective in air combat but proved particularly useful as a fighter-bomber. The Thunderbolt also served with a number of other Allied air arms. This document provides a history of the P-47 Thunderbolt.

[2] P-43 LANCER / XP-47B
[3] P-47B / P-47C
[5] P-47D / P-47G / XP-47K / XP-47L
[6] P-47D AT WAR
[7] XP-47H / XP-47J / P-47M / P-47N


* The P-47 Thunderbolt was, in a very indirect sense, a gift from Russia to the United States. The aircraft was the product of two Russian immigrants, Alexander De Seversky and Alexander Kartveli, who had left their homeland to escape the Reds.

Seversky was an extremely colorful character. He was born in 1894 in Russian Georgia, and became a naval aviator in the Tsar's forces in World War I. He lost a leg early in the conflict, but returned to the air with an artificial leg and claimed 13 "kills" in combat.

In 1918, after the October Revolution of 1917, Seversky was sent to the US as part of a military mission. Having no confidence in the new regime, he decided to stay in America, and became an aeronautical engineer in employ of the US Army Air Corps (USAAC), where he worked closely with air warfare pioneer General Billy Mitchell. Seversky obtained American citizenship in 1927.

In 1931, Seversky founded the "Seversky Aircraft Company" at Farmingdale on Long Island, in New York state. The company was very small, with Seversky acting as president, designer, and chief test pilot, but he also hired a fellow Russian expatriate named Alexander Kartveli as a design engineer. "Sasha" Kartveli had been a Tsarist artillery officer and had actually been a circus trapeze artist for a time. He was an original designer with many innovative ideas, and would eventually become chief designer when Seversky became more preoccupied with the business aspects of running a company.

* The first Seversky design was the "SEV-3" amphibian, The SEV-3 was an all-metal, low wing monoplane that was powered by Wright J-6 air-cooled radial engine providing 200 kW (420 HP), and had an interesting arrangement of retractable floats that allowed it to land on water or a runway. The rear edges of all flight surfaces were in the form of elliptical curves, a feature that would be retained in its ancestors. The "3" in the SEV-3 designation indicated that it was a three-seat aircraft. It was intended for commercial use.

First flight of the SEV-3 was in June 1933, with six production aircraft built. It was fast for its time, and in October 1933, Seversky set an international speed record of 290 KPH (180 MPH) with the prototype, which had been fitted with an uprated engine.

In 1934, the SEV-3 design was modified into a trainer configuration, designated the "SEV-3XAR". The float system was replaced by fixed landing gear with spats, the canopy was redesigned, and the engine was changed to a Wright R-975 radial with 710 kW (950 HP). The SEV-3XAR was entered in a USAAC competition for a flight trainer, and the Army ordered thirty examples of a derivative, the "BT-8 (Basic Trainer 8)".

Unfortunately, USAAC regulations required that the engine of a trainer must be limited to 300 kW (400 HP), and so the BT-8 was powered by a Pratt & Whitney (P&W) R-985-11 radial with that power rating. As a result, the aircraft was seriously underpowered and dangerous to inexperienced pilots, and was quickly replaced by the North American "BT-9", which evolved into the famous "AT-6 Texan" trainer.

* Although the BT-8 was a loser, Kartveli had also designed a fighter derivative of the SEV-3, initially designated "SEV-2M" but quickly redesignated "SEV-2XP", where the "2" indicated a two-seat aircraft.

The SEV-2XP used a Wright R-1670 14-cylinder air-cooled radial engine with 550 kW (735 HP) for take-off. It had fixed landing gear with spats, and was armed with a 7.62 millimeter (0.30 caliber) and a 12.7 millimeter (0.50 caliber) Browning machine gun firing through the propeller arc, plus a 7.62 millimeter Browning on a rearward-facing hand-held mount for use by the back-seater.

In May 1935, the USAAC announced a competition for a new single-seat fighter. Seversky believed the SEV-2XP could win, even though it was a two-seat fighter, and entered in the competition. However, the SEV-2XP was damaged in mid-June while flying to Wright Field in Ohio for the fly-off.

The SEV-2XP went back to the shop. Second thoughts arose about the aircraft's configuration, and so it was reworked into a single-seat fighter designated the "SEV-1XP". Along with the new single-seat cockpit and the elimination of the flexible gun, the fixed landing gear was changed to gear that retracted into underwing fairings. The Wright R-1670 had proven not powerful enough, and so, after experiments with different engine fits, the Seversky Company installed a P&W R-1830-9 Twin Wasp radial, with 635 kW (850 HP) for takeoff.

The Seversky Company was able to to make these changes because the USAAC postponed the fighter competition, with the fly-off rescheduled to March 1936. The SEV-1XP was entered in the competition, and ended up as a finalist against the Curtiss "Model 75 Hawk". The SEV-1XP was selected as the winner of the competition on 16 June 1936, and a production order for 77 of the aircraft, with the USAAC designation "P-35", was confirmed in early 1937. However, as tensions rose in Europe, the USAAC also ordered 210 Hawks under the designation "P-36".

* The actual P-35, which had the company designation "AP-1 (Army Pursuit 1)", entered service in 1937, with the last of the batch delivered in August 1938. 76 P-35s were actually built instead of the 77 ordered, with the 77th aircraft finished as an experimental variant for the USAAC, featuring a P&W R-1830-9 engine with a two-stage, two-speed supercharger and 895 kW (1,200 HP); better streamlining including fully retractable landing gear; and the designation of "XP-41".

The production P-35 differed from the SEV-1XP by featuring partial mainwheel fairings instead of full mainwheel fairings, seven degrees of dihedral to the outer wing panels, and a more aerodynamic front canopy.

   _____________________   _________________   _______________________
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                11 meters           36 feet
   wing area               20.44 sq_meters     220 sq_feet
   length                  7.67 meters         25 feet 2 inches
   height                  2.77 meters         9 feet 1 inch

   empty weight            1,960 kilograms     4,315 pounds
   normal loaded weight    2,540 kilograms     5,600 pounds

   max speed at altitude   454 KPH             282 MPH / 245 KT
   service ceiling         9,325 meters        30,600 feet
   range                   1,850 kilometers    1,150 MI / 1,000 NMI
   _____________________   _________________   _______________________

The P-35's performance was poor even by contemporary standards and its handling was atrocious, with a nasty tendency to go into a spin in any tight turn. Although USAAC fliers appreciated the P-35's ruggedness, the aircraft was already obsolescent by the time deliveries were finished.

* Kartveli continued to refine the P-35 design while the aircraft was being produced. The company constructed a range of one-off variants with different powerplants and enhancements, with the designations "AP-2", "AP-7", "AP-4" (which flew after the AP-7), "AP-9", and the previously mentioned XP-41; and actually built a carrier-based fighter designated the "NF-1 (Naval Fighter 1)".

None of these variants went into production and are of little interest, but the AP-4 proved significant in the further development of Seversky aircraft. It featured fully retractable landing gear, flush riveting, and most significantly a P&W R-1830-SC2G engine with a belly-mounted turbo-supercharger, providing 895 kW (1,200 HP) and good high-altitude performance. Exhaust-driven turbosupercharger technology had been refined by Boeing as part of the development program for the B-17 bomber, and the opportunities offered by it for improved performance were of great interest to other aircraft manufacturers.

The one AP-4 built was used as a test platform to evaluate means of improving the aerodynamics of radial-engine fighters. It was fitted with a very large prop spinner and a tight-fitting engine cowling, following similar experiments that had been performed with the first production P-35. The AP-4's big spinner was later removed and a new tight-fitting cowling was fitted. Unsurprisingly, these measures led to engine overheating problems. On 22 March 1939, the engine caught fire in flight, the pilot had to bail out, and the AP-4 was lost. However, it would lead to bigger and better things, to be discussed in the next section.

* Incidentally, Seversky also built a refinement of the original two-seat fighter concept embodied by the SEV-2XP, resulting in the "SEV-2PA Guardian", apparently also referred to as the "X-BT", which was available with retractable landing gear or floats. The USSR bought one with each landing gear option, plus a manufacturing license, but never put the type into production.

The Japanese Imperial Navy actually bought 20 SEV-2PAs, apparently through an intermediary as a subterfuge to conceal the ultimate customer, but found them disappointing. Two of them were passed on the ASAHI SHINBUM newspaper as hacks. Sweden ordered 52 SEV-2PAs as dive-bombers, but only two were delivered before the US embargoed exports of fighters to Sweden in October 1940. The other 50 ended up in USAAC hands as the "AT-12" and were used as gunnery trainers.

* The Seversky Company also sold Sweden a refinement of the P-35 designated the "EP-1 (Export Pursuit 1)". The EP-1 was powered by a P&W R-1830-S1C1 Twin Wasp engine with 745 kW (1,000 HP), improving its performance relative to the P-35 by over 40 KPH (25 MPH). The Swedes ordered a total of 120 EP-1s, with initial order placed in mid-1939.

60 of these aircraft were actually delivered to Sweden. They were armed with two 7.9 millimeter guns in the nose and one 13.2 millimeter gun in each wing, for a total of four guns. They served with the Swedish air force through the war and occasionally escorted intruding Allied bombers into internment, though they could barely keep up with the intruders and were at substantial risk of being shot down, as the EP-1 looked quite a bit like a German Focke-Wulf FW-190 fighter from some angles.

After the embargo against Sweden, the other 60 EP-1s were taken over by the USAAC as the "P-35A". They were apparently fitted with two 12.7 millimeter Brownings in the cowling and a 7.62 millimeter Browning in each wing. 48 were sent to the Philippines, where they fought in the futile defense of the islands in December 1941 and January 1942, but they were hopelessly outclassed by Japanese fighters. The other P-35As were used as USAAC trainers.


[2] P-43 LANCER / XP-47B

* On 13 October 1939, the Seversky Aircraft Company changed its name to the "Republic Aviation Company" after the stockholders bought out Seversky's holdings in the company. The firm's efforts to that time had done nothing that would win it a place in the history books, but that would soon change.

Although the turbo-supercharged AP-4 demonstrator had been lost, the USAAC liked it enough to order thirteen more in May 1939, to be designated "YP-43". However, USAAC requirements led to many modifications, and the YP-43 ended up looking much different from the AP-4. The YP-43 was powered by a P&W R-1830-35 14-cylinder Twin Wasp radial engine with turbo-supercharger, providing 895 kW (1,200 HP) and driving a three-blade propeller. Armament consisted of two 12.7 Brownings in the nose, plus a single 7.62 Browning in each wing. The cockpit scheme was revised, leading to a distinctive "razorback" configuration, as it would later be called.

* The first of the thirteen YP-43s was delivered in September 1940, and the last was delivered in April 1941. In the meantime, Republic had been working on a new version of the YP-43 with a more powerful engine, to be named the "XP-44 Rocket", as well as on a fighter designated the "AP-10" that was a considerable departure for Republic Aviation. The AP-10 was to be a lightweight fighter, powered by an Allison V-1710 watercooled inline engine and armed with a pair of 12.7 millimeter guns. The Army backed the project and ordered two prototypes in November 1940 in somewhat different configurations as the "XP-47" and "XP-47A".

However, by this time the war in Europe was in high gear, and the USAAC decided that the company's current fighter concepts were not good enough to deal with current German fighters. Alexander Kartveli went back to the drawing board and came up with what looked like a much bigger and badder version of the YP-43. The Air Corps decided they liked it and ordered a prototype, to be designated "XP-47B". The XP-47A, which had almost nothing in common with the new design, was abandoned.

The USAAC must have swallowed hard when they saw the design for the XP-47B for the first time. It was a monster. Kartveli is said to have remarked: "It will be a dinosaur, but it will be dinosaur with good proportions." Empty weight was 4,490 kilograms (9,900 pounds), or 65% more than the YP-43. The new aircraft was to be powered by a P&W R-2800 Double Wasp 18-cylinder two-row radial engine, with 1,490 kW (2,000 HP), linked to a hefty system of ductwork leading back to a turbo-supercharger inside the rear fuselage. Armament was to be eight 12.7 Brownings, with four in each wing.

* The XP-47B appeared to be what the USAAC wanted, and so the XP-44 Rocket was abandoned along with the XP-47A. However, the new fighter wouldn't go into production for some time, so to keep Republic's production lines in operation the Air Corps ordered 54 production P-43s.

Delays occurred in the XP-47B program, so the Air Corps another batch of 80 "P-43As", with a slightly different engine fit. Further delays led to yet another order for 125 "P-43A-1s" intended as Lend-Lease aircraft for China, with this last batch featuring armament of four 12.7 millimeter Brownings and self-sealing fuel tanks.

   _____________________   _________________   _______________________
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                11 meters           36 feet
   wing area               20.81 sq_meters     224 sq_feet
   length                  8.67 meters         28 feet 6 inches
   height                  4.27 meters         14 feet

   empty weight            2,600 kilograms     5,730 pounds
   loaded weight           3,540 kilograms     7,800 pounds

   max speed at altitude   575 KPH             355 MPH / 310 KT
   service ceiling         26,000 meters       26,000 feet
   range                   1,290 kilometers    800 MI / 695 NMI
   _____________________   _________________   _______________________

Including the thirteen YP-43As, a total of 272 P-43s of all types were delivered by the time of the last delivery in March 1942. The ultimate fate of all these aircraft is a bit fuzzy, mostly because the "Lancer", as it was known, was so forgettable. At least 51 did make it to China, and some served with Claire Chennault's American Volunteer Group, the "Flying Tigers", but the turbo-supercharger and the self-sealing tanks were unreliable and the type was not used much.

Most of the rest were converted into photo-reconnaissance aircraft, and a handful of these photo-reconnaissance Lancers were provided to Australia. These aircraft appear to have been given designations such as "P-43B", "P-43C", and "P-43D", with all then redesignated "RP-43" (where the "R" stood for "restricted from combat") in the fall of 1942, but the details are both unclear and uninteresting. The type saw little combat in any capacity. The P-43's only real significance was as a stepping stone to something better, and a way of keeping Republic's production lines going until they could deliver the new XP-47B.

* The XP-47B first flew on 6 May 1941, with Lowry P. Brabham at the controls. Although there were minor problems, such as a slight amount of cockpit smoke that turned out to be due to an oil drip, the aircraft proved impressive in its first trials.

The XP-47B was essentially built around the big Double Wasp and its turbo-supercharger. The loss of the AP-4 put an end to Kartveli's experiments with tight-fitting cowlings, so the engine was placed in a broad cowling that opened at the front in a "horse collar" shaped ellipse. The cowling admitted air for the engine, left and right oil coolers, and the turbo-supercharger intercooler system.

The engine's exhausts were routed into a pair of pipes that ran along each side of the cockpit to drive the turbo-supercharger turbine, which sat in the bottom of the fuselage about halfway between cockpit and tail. At full power, the pipes glowed red at their forward ends.

A "waste gate" shutter either vented the exhaust gas directly to the surrounding atmosphere, or, at higher altitudes, drove it through the turbo-supercharger turbine, spinning it at 60,000 RPM. The turbo-supercharger's intake was fed by ducting at the bottom of the fuselage leading to the front of the aircraft, with the ducting run through an "intercooler" that dumped waste heat into the airflow to increase power.

The complicated turbo-supercharger scheme with its ductwork gave the XP-47B a deep fuselage, and the wings had to be mounted at a relatively high position. This was a problem, since to take advantage of the powerful R-2800 engine, the aircraft was fitted with a huge four-bladed, electrically operated, constant-speed Curtiss propeller with a span of 3.17 meters (12 feet 2 inches). This meant that the XP-47B needed long landing gear to ensure adequate prop clearance on the ground, but long landing gear had to be very rugged and heavy, and also took up excessive space in the wing. As Kartveli wanted to put the aircraft's guns in the wings outboard of the landing gear, that wasn't acceptable, and so the main landing gear featured a remarkable scheme by which they telescoped out 23 centimeters (9 inches) when they were extended.

There were four 12.7 millimeter Browning machine guns in each wing, with the positions of the guns staggered to allow feed from ammunition boxes set side by side in the outer sections of the wings. Each ammunition box had a maximum capacity of 350 pounds of ammunition.

Main and auxiliary self-sealing fuel tanks were placed under the cockpit, offering a total fuel capacity of 1,155 liters (305 US gallons). This was a large fuel capacity for the time, but it would not prove to be enough.

The cockpit was roomy, as might be hoped for such a big machine, and the pilot's seat was comfortable, "like a lounge chair" as one pilot would later put it. The pilot was provided with every convenience, including cabin air conditioning.

The prototype featured a car-style door to get in and out, though this would be quickly abandoned in production machines in favoring a canopy that slid back over the aircraft's spine. The aircraft was of all-metal construction, except for fabric-covered tail control surfaces. The fabric-covered control surfaces would troublesome.


[3] P-47B / P-47C

* The XP-47B gave the USAAF (the "Air Forces" superseded the "Air Corps" in June 1941) cause for both optimism and apprehension. Aircraft performance and firepower appeared to be everything asked for, but the XP-47B was a something very new, and as a result it had it share of teething problems.

Its sheer size and power made it a handful. The XP-47B was also an "earth lover", demanding a lot of runway to get into the air. This would not only be true for every other P-47 ever built, but also with Kartveli's later jet designs. There were problems with canopies that jammed, with the guns, with the fuel system, with the engine installation. At high altitudes, the ignition system arced, and the loads on the control surfaces became unacceptable, the ailerons locking up. The fabric-covered control surfaces also tended to rupture at high altitudes due to the air stored in them.

Republic addressed the problems, coming up with a sliding canopy that could be discarded in an emergency, a pressurized ignition system, and new all-metal control surfaces. While the engineers worked frantically to get their "dinosaur" to fly right, the USAAF had to think hard and ask themselves if they really wanted the P-47.

The answer was YES, and the USAAF ordered 171 production "P-47Bs". An engineering prototype P-47B was delivered in December 1941, with a production prototype following in March 1942, and the first actual production model provided in May. Republic continued to tweak the design as P-47Bs were produced, adding the sliding canopy, a new General Electric (GE) turbo-supercharger regulator for the R-2800-21 engine, and (eventually) all-metal control surfaces. The radio mast behind the cockpit was slanted forward to maintain the aerial wire length with the new sliding canopy, providing a recognition feature for the variant.

The aircraft now had a name: "Thunderbolt". In postwar sources it would acquire the nickname of "Jug", said to be due to its resemblance to a jug of booze; as a contraction of "juggernaut"; or in reference to a "thunderjug", meaning a chamberpot. However, some sources claim this nickname was not in common use during the war and that the only nicknames it had during the conflict were "Bolt" or "T-Bolt". The matter of nicknames might as well be ignored, as it is very confusing and an example of how historical studies sometimes seem to only muddy the facts.

* Initial deliveries of the Thunderbolt to the USAAF were to the 56th Fighter Group (FG), which was also on Long Island. The 56th served as an operational evaluation unit for the new fighter.

Teething problems continued. A Republic test pilot was killed in an early production P-47B when it went out of control in a dive, and there were many crackups with other early P-47Bs, including crashes that occurred when the tail assembly fell off! Production changes gradually addressed the problems, but the original XP-47B was lost in August 1942 when it caught in fire in flight, forcing the pilot to bail out.

On the balance, though, with experience the USAAF decided that the P-47 was worthwhile, and quickly followed the initial order for P-47Bs for 602 more examples of a refined type, the "P-47C", with the first of the variant delivered in September 1942. The initial P-47Cs were very similar to the P-47B, but had strengthened all-metal control surfaces, a stronger tail, a short vertical radio mast, and other tweaky changes.

After the initial manufacture of a block of 57 P-47Cs, production moved to the "P-47C-1", which had a 20 centimeter (8 inch) fuselage extension forward of the cockpit. This corrected center of gravity problems and improved access to the engine. There were a number of other minor changes. 55 P-47C-1s were built, to be followed by 128 "P-47C-2s", which were identical except for a belly attachment point for either a 225 kilogram (500 pound) bomb or, more generally, a 758 liter (200 US gallon) conformal belly ferry tank. The P-47C-2 was really the first combat-ready Thunderbolt.

The main production P-47C subvariant was the "P-47C-5", featuring a whip antenna replacing the mast antenna, plus cockpit heating and other small changes. 362 were built. The P-47C-2 and P-47C-5 were the first Thunderbolts to be sent overseas for combat operations.

* The P-47B not only led to the P-47C but to a few other "one off" variants. A single reconnaissance variant designated "RP-47B" was built. The 171st and last P-47B was also used as an evaluation platform under the designation "XP-47E" to test the uprated R-2800-59 engine, a pressurized cockpit, and eventually a new Hamilton Standard propeller. Another P-47B was later fitted with new "laminar flow" wings in a search for higher performance and redesignated "XP-47F", but nothing came of this experiment.



* By the end of 1942, most of the troubles with the P-47 had been worked out, the American war machine was coming on line, and P-47Cs were sent to England for combat operations. The 56th FG was sent overseas to join the Eighth Air Force, whose 4th and 78th Fighter Groups were equipped with the Thunderbolt as well.

The 4th FG was built around a core of experienced American pilots who had served with the British Royal Air Force (RAF) before the war in the famous "Eagle Squadron". They were not too pleased to trade their Spitfires for the big Thunderbolt.

Indeed, their British counterparts were astounded when they saw the huge fighter, as it hardly seemed such a big aircraft could get off the ground, much less engage in air combat. The British joked that a Thunderbolt pilot could defend himself from a Luftwaffe fighter by running around and hiding in the fuselage.

Few American pilots were neutral about the Thunderbolt; they either hated it or loved it. On the negative side, there was the unpleasantly long take-off run, and the P-47 was not particularly maneuverable, though it was surprisingly agile at high altitudes. One Thunderbolt pilot compared it to flying a bathtub around the sky. A dead-stick landing with the P-47 was likely an unpleasant exercise.

On the positive side, it was rugged and well armed. It was a stable gun platform and its eight 12.7 Brownings could pour out a heavy volume of lead, and pilots reported targets unlucky enough to be caught in a P-47's crosshairs as simply exploding or disintegrating.

The Thunderbolt could also drop like a brick, which was an advantage in air battles. Luftwaffe pilots would find out that trying to break off combat and dive away was sheer suicide when fighting a Thunderbolt. The P-47 could easily reach 885 KPH (550 MPH) in a dive, and some Thunderbolt pilots claimed it could even break the sound barrier, but it appears that the airspeed indicator simply went crazy at high speeds.

Anyone could see that an aircraft as heavy as a Thunderbolt was likely to be fast in a dive, but more surprisingly it was hard to outclimb it. Even though the P-47 was big and heavy, its big R-2800 engine and huge propeller gave it a remarkable rate of climb. It also had an excellent rate of roll.

The P-47's first combat mission was on 10 March 1943, when the 4th FG took their aircraft on a fighter sweep over France, which was a fiasco due to radio malfunctions. The P-47s were all refitted with British radios, and missions resumed on 8 April 1943. The P-47 first mixed it up with the Luftwaffe on 15 April, with Major Don Blakeslee of the 4th FG scoring the Thunderbolt's first kill, shooting down an FW-190. On 17 August 1943, the P-47 performed its first escort mission, when it guarded a B-17 force on the first leg of a raid on Schweinfurt, Germany.

By the summer of 1943, the P-47 was also in service with the 12th Air Force in Italy. It was also fighting against the Japanese in the Pacific, with the 348th FG flying escort missions out of Brisbane, Australia.


[5] P-47D / P-47G / XP-47K / XP-47L

* Refinements of the Thunderbolt continued, leading to the definitive "P-47D". 12,602 P-47Ds were built, though the "D" model actually consisted of a series of subvariants, the last of which were visibly different from the first.

The first P-47Ds were actually the same as P-47C-2s. Republic could not produce Thunderbolts fast enough at its Farmingdale plant on Long Island, and so a new plant was built at Evansville, Indiana. The Evansville plant built a total of 110 P-47Ds, which were completely identical to P-47C-2s. By the way, Farmingdale aircraft were given a "-RE" suffix, while Evansville aircraft were given a "-RA" suffix, but this scheme is not used in this document, except when necessary for clarity.

The P-47D was built in a very large number of subvariants. Some of the subvariants were manufactured only at Farmingdale, some were only manufactured at Evansville, some were manufactured at both plants. The changes in subvariants were often minor and a detailed description of them all is tedious, but it is useful to point out the highlights. Note that there were breaks in the subvariant numbering sequence, and though the last of them was the P-47D-40, forty different subvariants were not produced.

The "P-47D-1" through "P-47D-6", the "P-47D-10", and the "P-47D-11" successively incorporated changes such as the addition of more engine cooling flaps around the back of the cowl, which greatly reduced the engine overheating problems that had been seen in the field; uprated engines and engine subsystems; refinements to fuel, oil, hydraulic systems; and additional armor protection for the pilot.

The "P-47D-15" was a large step forward, produced in response to requests by combat units for more range. The internal fuel capacity was increased to 1,421 liters (375 US gallons), and the wings were "plumbed" to allow a drop tank to be carried under each wing, in addition to the belly tank.

A variety of different drop tanks were fitted to the Thunderbolt during its career. Following the early conformal 758 liter (200 US gallon) ferry tank and the lozenge-shaped flat 758 liter belly tank, teardrop-shaped 284 liter (75 US gallon) and 568 liter (150 US gallon) metal wing drop tanks were adopted. The P-47 also used British-designed 409 liter (108 US gallon) and 758 liter tanks made of plastic-impregnated paper. These tanks were cheap and were useless to the enemy if found after being dropped, though they could not store fuel for an extended period of time. With the increased fuel capacity, the P-47 was now able to perform missions deep into enemy territory. The P-47D-15 could carry up to 1,130 kilograms (2,500 pounds) of external stores.

The "P-47D-16", "P-47D-20", "P-47D-22", and "P-47D-23" were similar to the P-47D-15 with minor improvements in fuel system, engine subsystems, a jettisonable canopy, bulletproof windshield, and so on. The 3.71 meter (12 foot 2 inch) Curtiss propeller was replaced by new and bigger propellers, the Long Island plant moving to a Hamilton Standard propeller with a diameter of 4.01 meters (13 feet 1-7/8 inches), and the Evansville plant moving to a new Curtiss propeller with a diameter of 3.96 meters (13 feet). The new propellers further boosted the climb rate, and Luftwaffe pilots found they couldn't get away from the P-47 by climbing.

Achieving ground clearance on take-off for the propeller had been troublesome in the XP-47B. With the bigger propellers, Thunderbolt pilots had to learn to be careful on takeoffs to keep the tail down until they obtained adequate ground clearance. Failure to do so caused the prop to divot the runway.

* Even with two Republic plants rolling out the P-47, the USAAF still wasn't getting as many Thunderbolts as they wanted, and so an arrangement was made with Curtiss to build the P-47 under license in a plant in Buffalo, New York. Most of the Curtiss Thunderbolts were intended for use in advanced flight training.

The Curtiss aircraft were all designated "P-47G", and a "-CU" suffix was used to distinguish them from other production. The P-47Gs were all identical to various P-47C and P-47D blocks, with the block equivalents and production quantities broken down as follows:

   P-47G:     P-47C       20
   P-47G-1:   P-47C-1     40
   P-47G-5:   P-47D-1     60
   P-47G-10:  P-47D-5     80
   P-47G-15:  P-47D-10   154 

   total P-47G:          354
Two of the P-47G-15s were built with the cockpit extended forward to just before the leading edge of the wing to provide twin tandem seating, and designated "TP-47G". The second crew position was accommodated by substituting a much smaller main fuel tank. The "Doublebolt" didn't go into production, but two-seat modifications were made in the field to older P-47s, which were then used as hacks. The cockpit was not moved forward on these improvised Doublebolts.

* All the P-47s produced to this time had the razorback canopy configuration, which was a source of complaints as it left pilots with poor visibility in the vital "6:00" position to the rear. The British also had this problem with their fighter aircraft, and had devised the bulged "Malcolm hood" canopy for the Spitfire as an initial solution. This was field-fitted to many North American P-51 Mustangs and, it seems, to a handful of P-47Ds.

However, the British then came up with a much better solution, devising an all-round vision "bubble" canopy for the Hawker Tempest. USAAF officials liked the bubble canopy, and quickly adapted it to American fighters, including the P-51 and the Thunderbolt. The initial P-47 with a bubble canopy was completed in the summer of 1943. It was modified from the last production P-47D-5, and was designated "XP-47K". Another older P-47D had been modified to provide an internal fuel capacity of 1,402 liters (370 US gallons) and given the designation "XP-47L". The bubble top and increased fuel capacity were then rolled into production together, resulting in the "P-47D-25".

It was followed by similar bubble-top variants, including the "P-47D-26", "P-47D-27", "P-47D-28", and "P-47D-30". Improvements added in this series included engine refinements, more internal fuel capacity, the addition of dive flaps, and other tweaky changes.

   REPUBLIC P-47D-25-RE:
   _____________________   _________________   _______________________
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                12.4 meters         40 feet 9 inches
   length                  11.0 meters         36 feet 1 inch
   height                  4.3 meters          14 feet 2 inches

   empty weight            4,850 kilograms     14,600 pounds
   max loaded weight       8,800 kilograms     19,400 pounds

   maximum speed           690 KPH             428 MPH / 372 KT
   service ceiling         12,000 meters       40,000 feet
   range                   3,060 kilometers    1,900 MI / 1,725 NMI
   _____________________   _________________   _______________________

   Maximum speed is given for an altitude of 9,000 meters (30,000 feet).
   Range is with three drop tanks.

The "P-47D-40" was the final P-47D subvariant, and was a more significant update. Cutting down the rear fuselage to accommodate the bubble canopy had led to yaw instability in the aircraft's flight, so the P-47D-40 had a neat dorsal fin extension in the form of a narrow triangle running from the vertical tailplane to the radio aerial. The dorsal fin extension was retrofitted in the field to earlier P-47D bubble-top variants.

The P-47D-40 also featured provisions for ten "zero length" stub launchers for 12.7 centimeter (5 inch) "High Velocity Air Rockets (HVARs)", as well as the new "K-14" computing gunsight. This was a license-built copy of the British Ferranti GGS Mark IID computing gyro sight, which allowed a pilot to dial in target wingspan and range, and would then tell the pilot when he had a good shot at the target. The K-14 was a great assistance in deflection shooting, earning the nickname of "ace-maker", though pilots who were "naturals" at deflection shooting tended to find it a complicated bother.


[6] P-47D AT WAR

* The P-47D, as the first really satisfactory version of the Thunderbolt and the most heavily produced variant by far, bore the brunt of the P-47's combat service.

By 1944, the Thunderbolt was in combat with the USAAF in all its operational theaters, except Alaska. With increases in fuel capacity as the type was refined, the range of escort missions over Europe steadily increased until the P-47 was able to accompany bombers in raids all the way into Germany itself.

On the way back from raids, pilots shot up targets of opportunity, which led to the realization that the P-47 made an excellent fighter-bomber. Even with its complicated turbosupercharger system, it could absorb a lot of damage, and its eight machine guns meant it could cause a lot of damage as well. Armor-piercing rounds could even chew up a German Tiger tank, smashing into the relatively thin top armor on top and bouncing off the road to penetrate the belly.

Gradually, the P-47 became the USAAF's best fighter-bomber, carrying 225 kilogram (500 pound) bombs, sometimes with extended "daisy cutter" fuzes to provide greater blast effect against exposed targets; napalm tanks; the triple-tube M-8 11.5 centimeter (4.5 inch) rocket launcher, which was inaccurate; and eventually the much-better HVAR. Thunderbolts were one of the mainstays of the USAAF in tactical support of the Normandy landings, and continued the tradition through the rest of the war, destroying thousands of tanks, locomotives, and parked aircraft, and tens of thousands of trucks and other vehicles.

The P-51 Mustang gradually replaced the Thunderbolt in the long-range escort role as the Mustang had superior range and a more comfortable cockpit. However, the P-47 still ended the war in Europe with impressive scores in air combat. Lieutenant Colonel Francis S. "Gabby" Gabreski scored 31 kills, Captain Robert S. "Bob" Johnson scored 28, and Colonel H. "Pop" Zemke scored 20. It is a tribute to the aircraft's ruggedness that all ten of the top-scoring Thunderbolt aces survived the war.

Some Thunderbolts were modified to a "Superbolt" configuration to improve their performance in air combat. The Superbolts had half their guns and some armor removed, featured engine modifications to allow them to burn higher-octane fuel, and featured a highly polished finish.

Some war-weary P-47s were actually used in the air-sea rescue (ASR) role, carrying a rubber life raft in a pack under each wing and carrying flares under the rear fuselage to mark the position of downed aircrew. They went into service in this role in the spring of 1944. The ASR Thunderbolts retained most or all of their gun armament, and one shot down a German V-1 flying bomb.

* The Thunderbolt also provided extensive service against the Japanese, by both the USAAF and the British. The RAF began to receive the type during mid-1944, and received 240 razorback P-47Ds, which they designated "Thunderbolt Mark I", and 590 bubbletop P-47Ds, which they designated "Thunderbolt Mark II".

Except for a few evaluation aircraft, these were all operated by the RAF from India for ground-attack operations, known as "cab rank" sorties, against the Japanese in Burma. They were armed with 225 kilogram (500 pound) bombs, or in some cases the British "60-pounder" rocket projectiles. As the Thunderbolt resembled the Japanese Nakajima Ki-44-II Shoji ("Tojo") fighter, RAF Thunderbolts were often painted with white "recognition bands", and recognition markings were also adopted by USAAF Thunderbolts operating in the theater. The Thunderbolts remained in RAF service for a short time after the war, the last of them being phased out of service in October 1946.

The Brazilian Air Force received 88 P-47Ds, and flew them in combat during the Italian campaign. Mexico received 25 for operations against Japan and flew a squadron in combat over the Pacific under USAAF command. The Free French received 446 P-47Ds beginning in March 1944, with these machines supporting the drive through southern France and into Germany. French Thunderbolts would also see action in the 1950s during the insurrection in Algeria.

203 P-47Ds were also provided to the Soviet Union. There was a certain irony in sending aircraft designed by a Russian emigre back to Russia. The Soviets were unimpressed with the P-47. It could not match the agility of the lighter Soviet fighters, while it could not compete with the heavily armored purpose-designed Il-2 Shturmovik in the close-support role.

The Luftwaffe operated at least three captured P-47s. They were used for comparative evaluation, in propaganda films, and may have been used on reconnaissance missions over the UK.


[7] XP-47H / XP-47J / P-47M / P-47N

* Although the P-47D was the high point of the Thunderbolt's career in terms of quantity and use, there were further attempts to refine the type.

Two "XP-47Hs" were built. They were major reworkings of existing razorback P-47D to accommodate a Chrysler XI-2220-11 water-cooled inline 16-cylinder inverted vee engine. Really big inline engines didn't prove to be a good idea in general, and the XP-47H went nowhere.

The "XP-47J" began as a November 1942 request to Republic for a "hot rod" version of the Thunderbolt, using a lighter airframe and an uprated engine with water injection and fan cooling. Kartveli designed an aircraft fitted a tight-cowled Pratt & Whitney R-2800-57(C) engine with a war emergency rating of 2,090 kW (2,800 HP), reduced armament of six machine guns, a new and lighter wing, and many other changes.

The first and only XP-47J was first flown in late November 1943, but by this time Republic had moved on to a new concept, the "XP-72", described in the next section, and the XP-47J was used mainly as a test machine. With various refinements, such as a GE CH-5 turbosupercharger, this aircraft achieved a top speed of 813 KPH (505 MPH) in level flight in August 1944, making it one of the fastest piston engine fighters ever built. However, the new jet aircraft being designed were clearly capable of much better performance, and the XP-47J was a dead end.

* The "P-47M" was a more conservative attempt to come up with a "hot rod" version of the Thunderbolt. Three P-47Ds were modified into prototype YP-47Ms by fitting the P&W R-2800-57(C) engine and the GE CH-5 turbosupercharger.

The performance of the YP-47M was excellent, with a top speed of 761 KPH (473 MPH), and the variant was rushed into production to counter the threat of the new German V-1 cruise missiles and German jet fighters. 130 P-47Ms were built, with the first arriving in Europe in early 1945. However, the type suffered persistent teething problems in the field and did not see much action until the war was all but over.

* The "P-47N" was the last Thunderbolt variant to be produced, and was intended for operations in the Pacific theater. A fighter was needed to escort Boeing B-29 Superfortress bombers in raids on the Japanese home islands, flown over long stretches of the Pacific.

Increased internal fuel capacity and drop tanks had done much to extend the Thunderbolt's range during its evolution, but the only way to cram more fuel into the aircraft was to put fuel tanks into the wings. This required a completely new wing, with each wing accommodating two 190 liter (50 US gallon) fuel tanks.

The second YP-47M was fitted with the new wing and flew in September 1944. The redesign proved successful in extending range to about 3,200 kilometers (2,000 miles), and the fact that the new wing, though longer than the old, had squared-off rather than elliptical wingtips improved the aircraft's roll rate.

The P-47N entered mass production with the uprated P&W R-2800-77(C) engine, beginning with the "P-47N-1", then the "P-47N-5", the "P-47N-15", the "P-47N-20", and the "P-47N-25", with a variety of small changes, such as a distinctive raised dorsal fin extension.

A total of 1,816 P-47Ns were built. The very last Thunderbolt to be built, a P-47N-25, rolled off the production line in October 1945. Thousands more had been on order, but production was essentially cut off with the end of the war in August. At the end of production, cost of a Thunderbolt was $83,000 USD in 1945 dollars.

Although the P-47N had been designed for the Pacific theatre, early production of the variant was sent to England, though the war ended before they could see much action. P-47Ns arrived on Saipan in the spring of 1945 and conducted their intended escort missions, though they were more generally used in the fighter-bomber role.



* One of the interesting dead-end variants of the P-47 was the XP-72, which was designed as a "Super Thunderbolt" that pushed the top limits of piston fighter development. It was powered by the 28-cylinder Pratt & Whitney Wasp Major air-cooled four-row 28-cylinder radial engine, providing 2,575 kW (3,450 HP) at altitude.

The XP-72 looked like a Thunderbolt, except for the fuselage ahead of the cockpit. The big Wasp Major engine was in a close-fitting cowl and capped with a big prop spinner, and the airscoop was moved back to just under the leading edge of the wings. The XP-72 was armed with six 12.7 millimeter Brownings, and could carry a 450 kilogram (1,000 pound) bomb under each wing.

   _____________________   _________________   _______________________
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                12.5 meters         40 feet 11 inches
   wing area               27.87 sq_meters     300 sq_feet
   length                  11.2 meters         36 feet 7 inches
   height                  4.42 meters         14 feet 6 inches

   empty weight            4,970 kilograms     10,965 pounds
   loaded weight           6,690 kilograms     14,750 pounds

   max speed at altitude   790 KPH             490 MPH / 425 KT
   service ceiling         12,800 meters       42,000 feet
   range                   1,930 kilometers    1,200 MI / 1,045 NMI
   _____________________   _________________   _______________________

The USAAF signed a contract for two XP-72 prototypes in June 1943, and the first prototype flew on 2 February 1944. The first prototype had a big four-blade propeller. The second prototype first flew in July 1944, and was generally similar but used a contra-rotating six-blade propeller to deal with the tremendous torque.

The second prototype was lost early in its flight test program, but the XP-72 was a very impressive aircraft, with excellent performance and a tremendous rate of climb. In fact, the USAAF ordered 100 production P-72s, apparently to be armed with four 37 millimeter cannon, but even as the XP-72 was proving its merits the Air Force was realizing that the new jet aircraft offered far better performance. The contract was cancelled and the first prototype was scrapped at the end of the war.

* The P-47 soldiered on after the war, serving with USAF (the Army Air Force became the Air Force in 1947) until 1949, and then with the US Air National Guard until 1953, with the designation "F-47" from 1948. The type was provided to many Latin American air arms and was operated by them through the 1950s, and some used it well into the 1960s. Small numbers of Thunderbolts were also provided to China, Iran, Turkey, and Yugoslavia.

A total of 15,660 Thunderbolts of all types were built, making it one of the most heavily produced fighter aircraft in history. A number of P-47s have survived to the present day, and at least ten are still flying.



* One of the fun and tricky things about this writeup was trying to figure out the complicated engine and turbosupercharger layout of the Thunderbolt. I had a verbal description, but I had to read it a sentence at a time and then consult a cutaway diagram of the aircraft so I could see just what exactly was going on.


* Revision history:

   v1.0   / 01 jan 00 / gvg
   v1.1   / 01 may 01 / gvg / Minor cleanup and update.
   v1.2.0 / 01 jun 03 / gvg / Minor cleanup and update.