The Republic P-47 Thunderbolt, also known as the Jug, was the largest single-engined fighter of its day, and a vast improvement over the Curtiss P-40 Warhawk, its predecessor. It was one of the main United States Army Air Force (USAAF) fighters of World War II, and also served with other Allied air forces. The P-47 was effective in air combat but proved especially adept at ground attack. It had eight .50-caliber machine guns, four per wing. When fully loaded the P-47 could weigh up to eight tons. A modern-day counterpart in that role, the A-10 Thunderbolt II, takes its name from the P-47.
In 1939, Republic Aviation designed the AP-4 demonstrator powered by a Pratt & Whitney R-1830 radial engine with a belly-mounted turbocharger. While the resulting P-43 Lancer was in limited production, Republic had been working on an improved P-44 Rocket with a more powerful engine, as well as on a fighter designated the AP-10. The latter was a lightweight aircraft powered by the Allison V-1710 liquid-cooled V-12 engine and armed with 8 .50-caliber (12.7 mm) machine guns. The United States Army Air Corps (USAAC) backed the project and gave it the designation XP-47.
As the war in Europe escalated in spring 1940, Republic and the USAAC concluded that the XP-44 and the XP-47 were inferior to the German fighters. Republic unsuccessfully attempted to improve the design, proposing the XP-47A. Alexander Kartveli subsequently came up with an all-new and much larger fighter which was offered to the USAAC in June 1940. The Air Corps ordered a prototype in September, to be designated the XP-47B. The XP-47A, which had almost nothing in common with the new design, was abandoned.
The XP-47B was all-metal construction (except for fabric-covered tail control surfaces) with elliptical wings. The cockpit was roomy and the pilot's seat was comfortable -- "like a lounge chair," as one pilot later put it. The pilot was provided with every convenience, including cabin air conditioning. The canopy doors hinged upward. Main and auxiliary self-sealing fuel tanks were placed under the cockpit, giving a total fuel capacity of 305 U.S. gallons (1,155 L).
Power came from a Pratt & Whitney R-2800 Double Wasp two-row 18-cylinder radial engine producing 2,000 hp (1,500 kW) and turning a four-bladed Curtiss Electric constant-speed propeller 146 inches (3.7 m) in diameter. The loss of the AP-4 prototype to an engine fire ended 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 cooling air for the engine, left and right oil coolers, and the turbosupercharger intercooler system. The engine exhaust gases were routed into a pair of wastegate-equipped pipes that ran along each side of the cockpit to drive the turbosupercharger turbine at the bottom of the fuselage about halfway between cockpit and tail. At full power, the pipes glowed red at their forward ends and the turbine spun at 60,000 revolutions per minute. The complicated turbosupercharger system with its ductwork gave the XP-47B a deep fuselage, and the wings had to be mounted in a relatively high position. This was problematic since long landing gear were needed to provide ground clearance for the propeller. To reduce the size and weight of the long landing gear and so that wing-mounted machine guns could be fitted, each main gear strut was fitted with an ingenious mechanism by which it telescoped out nine inches (230 millimeters) when extended.
The XP-47B was a very large aircraft for its time with an empty weight of 9,900 pounds (4,490 kg), or 65 percent more than the YP-43. Kartveli is said to have remarked, "It will be a dinosaur, but it will be a dinosaur with good proportions. The armament consisted of eight 0.50 caliber (12.7 mm) machine guns, four in each wing. The guns were staggered to allow feeding from side-by-side ammunition boxes, each with a 350-round capacity. Although the British already possessed eight-gun fighters in the form of the Hurricane and the Spitfire and the twelve-gun Hawker Typhoon, these used the smaller 0.303 caliber (7.7 mm) guns.
The XP-47B first flew on 6 May 1941 with Lowry P. Brabham at the controls. Although there were minor problems, such as some cockpit smoke that turned out to be due to an oil drip, the aircraft proved impressive in its first trials. It was eventually lost in an accident on August 8, 1942, but before that mishap the prototype had achieved a level speed of 412 mph (663 kph) at 25,800 ft (7,864 m) altitude, and had demonstrated a climb from sea level to 15000 ft altitude in five minutes.
The XP-47B gave the newly reorganized United States Army Air Forces cause for both optimism and apprehension. While possessing good performance and firepower, the XP-47B had its share of teething problems:
Republic addressed the problems with a sliding canopy that could be jettisoned in an emergency, a pressurized ignition system, and new all-metal control surfaces (improved engine-accessory access had to wait until the P-47C introduced a new engine mount). While the engineers worked frantically to get their "dinosaur" to fly right, the USAAF ordered 171 P-47Bs. An engineering prototype P-47B was delivered in December 1941, with a production prototype following in March 1942, and the first production model provided in May. Republic continued to improve the design as P-47Bs were produced, and although all P-47Bs had the sliding canopy and the new General Electric turbosupercharger regulator for the R-2800-21 engine, features such as all-metal control surfaces were not standard at first. A modification unique to the P-47B was the radio mast behind the cockpit that was slanted forward to maintain the originally designed antenna wire length in spite of the new sliding canopy.
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. In September 1942, the 171st and last P-47B (41-6065) was also used as a test platform under the designation XP-47E to evaluate the R-2800-59 engine, a pressurized cockpit with a hinged canopy and, eventually, a new Hamilton Standard propeller. The plans for production were cancelled after increased emphasis on low-level operations over Europe. Another P-47B was later fitted with a new laminar flow wing in search of higher performance and redesignated XP-47F.
Initial deliveries of the Thunderbolt to the USAAF were to the 56th Fighter Group, 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 crashes occurred due to failure of the tail assembly. The introduction of revised rudder and elevator balance systems and other changes corrected these problems. In spite of the problems, the USAAF was interested enough to order an additional 602 examples of the refined P-47C, with the first of the variant delivered in September 1942.
P-47Cs were sent to England for combat operations in late 1942. The 56th FG was sent overseas to join the Eighth Air Force, whose 4th and 78th Fighter Groups were soon to be equipped with the Thunderbolts. The 4th Fighter Group was built around a core of experienced American pilots, volunteers who had served with the British Royal Air Force (RAF) during 1941-43 in the Eagle Squadrons and who flew the Spitfire until January 1943. The 78th FG, formerly a P-38 group, also began conversion to the P-47 in January 1943. Commenting on the P-47's size, British pilots joked that a Thunderbolt pilot could defend himself from a Luftwaffe fighter by running around and hiding in the fuselage. Some British assumed the American P-47 nickname "Jug" was short for "Juggernaut" and began using the longer word as an alternate nickname. Another nickname that was used for the Thunderbolt was "T-bolt".
The first P-47 combat mission took place 10 March 1943 when the 4th FG took their aircraft on a fighter sweep over France. The mission was a failure due to radio malfunctions. All P-47s were refitted with British radios, and missions resumed 8 April. The first P-47 air combat took place 15 April with Major Don Blakeslee of the 4th FG scoring the Thunderbolt's first air victory. On 17 August, P-47s performed their first large-scale escort missions, providing B-17 bombers with both penetration and withdrawal support of the Schweinfurt-Regensburg mission, and claiming 19 kills against three losses.
By the summer of 1943, the Jug was also in service with the 12th Air Force in Italy, and it was fighting against the Japanese in the Pacific with the 348th Fighter Group flying escort missions out of Brisbane, Australia.
The first P-47Ds were actually the same as P-47Cs. Republic could not produce Thunderbolts fast enough at its Farmingdale plant on Long Island, 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. Farmingdale aircraft were identified by the "-RE" suffix after the block number, while Evansville aircraft were given the "-RA" suffix.
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 to reduce the engine overheating problems that had been seen in the field. Engines and engine subsystems saw refinement, as did the fuel, oil and hydraulic systems. Additional armor protection was also added for the pilot.
The P-47D-15 was produced in response to requests by combat units for increased range. The internal fuel capacity was increased to 375 U.S. gallons (1,421 L) and the bomb racks under the wings were made "wet" (equipped with fuel plumbing) to allow a jettisonable drop tank pressurized by vented exhaust air to be carried under each wing, in addition to the belly tank. Five different auxiliary tanks were fitted to the Thunderbolt during its career:
The tanks made of plastic-impregnated (laminated) paper could not store fuel for an extended period of time, but they worked quite well for the time it took to fly a single mission. These tanks were cheaper, lighter in weight, and were useless to the enemy if recovered after being dropped — not only did they break apart, but they did not provide the enemy with any reusable materials that could be scavenged for their own war effort. With the increased fuel capacity, the P-47 was now able to perform escort missions deep into enemy territory. A drawback to their use was that fighters could not land with the tanks in place because of the hazard of rupture and explosion. Fighters recalled from a mission or that did not jettison for some reason were required to drop paper tanks into a designated "dump" area at their respective fields, resulting in substantial losses of aviation fuel.
The P-47D-16, D-20, D-22 and D-23 were similar to the P-47D-15 with minor improvements in fuel system, engine subsystems, a jettisonable canopy, and bulletproof windshield. Beginning with the block 22 aircraft, the original narrow-chorded Curtiss propeller was replaced by propellers with larger blades, the Evansville plant switching to a new Curtiss propeller with a diameter of 13 feet (3.96 m) and the Long Island plant using a Hamilton Standard propeller with a diameter of 13 feet 2 inches (4.01 m). With the bigger propellers having barely six inches of ground clearance, Thunderbolt pilots had to learn to be careful on takeoffs to keep the tail down until they obtained adequate ground clearance, and on landings to flare the aircraft properly. Failure to do so damaged both the propeller and the runway.
Even with two Republic plants rolling out the P-47, the USAAF still was not getting as many Thunderbolts as they wanted, consequently, an arrangement was made with Curtiss to build the aircraft 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 first P-47G was completely identical to the P-47C, the P-47G-1 was identical to the P-47C-1, while the following P-47G-5, P-47G-10, and P-47G-15 sub-variants were comparable to the P-47D-1, P-47D-5 and P-47D-10 respectively. Two P-47G-15s were built with the cockpit extended forward to just before the leading edge of the wing to provide twin tandem seating, designated TP-47G. The second crew position was accommodated by substituting a much smaller main fuel tank. The "Doublebolt" did not go into production but similar modifications were made in the field to older P-47s, which were then used as squadron "hacks" (miscellaneous utility aircraft). Curtiss built a total of 354 P-47Gs.
All the P-47s to this point had a "razorback" canopy configuration with a tall fuselage spine behind the pilot which resulted in poor visibility 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 fitted in the field to many North American P-51 Mustangs, and to a handful of P-47Ds (and far more on P-47Bs and P-47Cs). However, the British then came up with a much better solution, devising an all-round vision "bubble" canopy for the Hawker Typhoon. USAAF officials liked the bubble canopy, and quickly adapted it to American fighters, including the P-51 and the Thunderbolt. The first P-47 with a bubble canopy was a modified P-47D-5 completed in the summer of 1943 and redesignated XP-47K. Another older P-47D was modified to provide an internal fuel capacity of 370 U.S. gallons (1,402 L) and given the designation XP-47L. The bubble canopy and increased fuel capacity were then rolled into production together, resulting in the block 25 P-47D (rather than a new variant designation). First deliveries to combat groups began in May 1944.
It was followed by similar bubble-top variants, including the P-47D-26, D-27, D-28 and D-30. Improvements added in this series included engine refinements, more internal fuel capacity, and the addition of dive recovery flaps. Cutting down the rear fuselage to accommodate the bubble canopy produced yaw instability, and the P-47D-40 introduced a dorsal fin extension in the form of a narrow triangle running from the vertical tailplane to the radio aerial. The fin fillet 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 5 inch (127 mm) High Velocity Aerial 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 gyroscopic sight which allowed the pilot to dial in target wingspan and range, and would then move the gunsight reticle to compensate for the required deflection.
The bubbletop P-47s were nicknamed "Superbolts" by combat pilots in the field.
By 1944, the Thunderbolt was in combat with the USAAF in all its operational theaters, except the Battle of the Aleutian Islands. 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. On the way back from the raids, pilots shot up ground targets of opportunity, and also used belly shackles to carry bombs on short-range missions, which led to the realization that the P-47 could perform a dual-function on escort missions as a fighter-bomber. Even with its complicated turbosupercharger system it could absorb a lot of damage, and its eight machine guns could inflict heavy damage on lightly armored targets. The P-47 gradually became the USAAF's best fighter-bomber, carrying the 500 pound (227 kg) bombs, the triple-tube M-8 4.5 inch (115 mm) rocket launchers, and eventually HVARs. From the invasion of Europe on 6 June 1944, to VE day on 7 May 1945, the Thunderbolt units claimed destroyed: 86,000 railway cars, 9,000 locomotives, 6,000 armoured fighting vehicles, and 68,000 trucks.
Although the P-51 Mustang replaced the P-47 in the long-range escort role in Europe, the Thunderbolt still ended the war with 3,752 air-to-air kills claimed in over 746,000 sorties of all types, at the cost of 3,499 P-47s to all causes in combat. In Europe in the critical first three months of 1944 when the German aircraft industry and Berlin were heavily attacked, the P-47 shot down more German fighters than did the P-51 (570 out of 873), and shot down approximately 900 of the 1,983 claimed during the first six months of 1944. In Europe, the Thunderbolt flew more sorties (423,435) than P-51s, P-38s and P-40s combined.
By the end of the war, the 56th FG was the only 8th Air Force unit still flying the P-47, by preference, instead of the P-51. The unit claimed 665.5 air victories and 311 ground kills, at the cost of 128 aircraft. Lieutenant Colonel Francis S. "Gabby" Gabreski scored 31 victories, including three ground kills, Captain Bob Johnson scored 27 (with one unconfirmed probable kill leading to some giving his tally as 28), and 56th FG Commanding Officer Colonel Hubert Zemke scored 17.75 kills. Despite being the sole remaining P-47 group in the 8th Air Force, the 56th FG remained its top-scoring group in aerial victories throughout the war.
In the Pacific, Colonel Neel E. Kearby of the 5th Air Force destroyed 22 Japanese aircraft and was awarded the Medal of Honor for an action in which he downed six enemy fighters on a single mission. He was shot down and killed over Biak in March 1944.
Two XP-47Hs were built. They were major reworkings of existing razorback P-47Ds to accommodate a Chrysler IV-2220-11 water-cooled 16-cylinder inverted vee engine. However, such large inline engines did not prove to be especially effective.
The XP-47J began as a November 1942 request to Republic for a high-performance version of the Thunderbolt using a lighter airframe and an uprated engine with water injection and fan cooling. Kartveli designed an aircraft fitted with a tight-cowled Pratt & Whitney R-2800-57(C) with a war emergency rating of 2,800 horsepower (2,090 kW), reduced armament of six 0.50 inch (12.7 mm) machine guns, a new and lighter wing, and many other changes. The first and only XP-47J was first flown in late November 1943. When fitted with a GE CH-5 turbosupercharger, the XP-47J achieved a top speed of 440 knots (505 mph, 813 km/h) in level flight in August 1944, making it one of the fastest piston engine fighters ever built. However, by that time Republic had moved on to a new concept, the XP-72.
The second YP-47M (of the batch of four converted P-47Ds) was later fitted with new wings and served as the prototype for the P-47N.
The P-47N was the last Thunderbolt variant to be produced. It was designed as an escort fighter for the B-29 Superfortress bombers flying raids on the Japanese home islands. Increased internal fuel capacity and drop tanks had done much to extend the Thunderbolt's range during its evolution, and the only other way to expand the fuel capacity was to put fuel tanks into the wings. Thus, a new wing was designed with two 50 U.S. gallon (190 L) fuel tanks. The second YP-47M with this wing flew in September 1944. The redesign proved successful in extending range to about 2,000 miles (3,200 km), and the squared-off wingtips improved the roll rate. The P-47N entered mass production with the uprated R-2800-77(C) engine, with a total of 1,816 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 halted with the end of the war in August. At the end of production, cost of a Thunderbolt was $83,000 in 1945 U.S. dollars.
The P-47 served with the Army Air Forces (United States Air Force after 1947) until 1949, and with the Air National Guard until 1953, receiving the designation F-47 in 1948. P-47s also served as spotters for rescue aircraft such as the OA-10 Catalina and Boeing B-17H.
The F-51 Mustang was used by the USAF during the Korean War, mainly in the close air support role. The F-47 was not deployed to Korea. Since the Mustang was more vulnerable to being shot down, (and many were lost due to anti-aircraft fire), some former F-47 pilots have suggested the more durable Thunderbolt should have been sent to Korea; however the F-51D was available in greater numbers in the USAAF/ANG inventories .
A total of 15,686 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 a few are still flying.
P-47s were operated by several Allied air arms during World War II. The RAF received 240 razorback P-47Ds which they designated "Thunderbolt Mark I," and 590 bubbletop P-47D-25s, designated "Thunderbolt Mark II"s. With no need for another high-altitude fighter, they were adopted for ground attack. Once the Thunderbolts were cleared for use in 1944, they were operated against the Japanese in Burma by 16 RAF squadrons of the South East Asia Command from India. Operations were Army support (operating as "cab rank"s to be called in when needed), attacks on enemy airfields and lines of communication, and escort sorties. The Thunderbolts were armed with three 500 pound (227 kg) bombs or, in some cases, British "60 pound" (27 kg) RP-3 rocket projectiles. Long range fuel tanks gave five hours of endurance. Thunderbolts remained in RAF service until October 1946; those squadrons not disbanded outright after the war re-equipped with British-built aircraft.
During the Italian campaign, the Brazilian Expeditionary Force flew a total of 67 P-47Ds in combat of which 15 were lost to German flak. The "1º Grupo de Aviação de Caça" (1st Brazilian Fighter Squadron) flew a total of 445 missions from November 1944 to May 1945, with 5 pilots being killed in action. In the early 80s the "1º Grupo de Aviação de Caça" was awarded the "Presidential Unit Citation" by the American Government in recognition for its achievements in WWII.
In 1945, the Mexican Escuadron Aereo de Pelea 201 (201st Fighter Squadron) operated P-47Ds as part of the U.S. Fifth Air Force in the Philippines. In 791 sorties against Japanese forces, the 201st lost no pilots or aircraft to enemy action.
Over Italy, in 1943–45, P-47s were initially met as enemies in fierce aerial battles. During the devastating attacks made by U.S. bombers over Fiat on 25 April 1944, three G.55s were downed by P-47s without loss, although the Italian fighters managed before to shoot down several bombers. In another battle in spring 1945, P-47s shot down five G.55s and C.205Vs downed for no losses. Postwar, the Italian Air Force (AMI) received 75 P-47D-25s (sent to 5˚ Stormo, and 99 to the 51˚). These machines were delivered between 1947 and 1950. From 1953 they were replaced by F-84s. AMI P-47s were not well liked as Italian pilots found them too heavy and too expensive to maintain. Nevertheless, the stability, payload and high speed were appreciated. Most importantly, they were a good platform to set up the transition to heavier jet fighters, including the F-84 Thunderjet, starting in 1953.
The Soviet Union also received 203 P-47Ds. The fighters were assigned to high-altitude air defense over major cities in rear areas. Unlike their Western counterparts, the Soviet Air Force made no notable use of the P-47 as a ground attack aircraft, depending instead on the P-39, P-63 and their own widely-produced Ilyushin Il-2.