Republic P-47 Thunderbolt
The Republic P-47 Thunderbolt, also known as the ‘Jug,’ was the biggest, heaviest, and most expensive fighter aircraft in history to be powered by a single piston engine. It was one of the main United States Army Air Forces (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 eight .50 in (12.7 mm) M2 Browning 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, with a straight leading edge that was slightly swept back. 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. gal (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 in (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 21,300 rpm. 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 9 in (23 cm) when extended.
The XP-47B was a very large aircraft for its time with an empty weight of 9,900 lb (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 in (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 12-gun Hawker Typhoon, these used the smaller 0.303 in (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 km/h) at 25,800 ft (7,864 m) altitude, and had demonstrated a climb from sea level to 15,000 ft (4,600 m) altitude in five minutes.
P-47B / P-47C / XP-47E / XP-47F
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:
* Its sheer size and limited ground-propeller clearance made for challenging takeoffs which required long runways - the pilot had to hold the tail low until considerable speed was attained on the initial run.
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.
Beginning in January 1943, Thunderbolt fighters were sent to the joint Army Air Forces-civilian Millville Airport in Millville, New Jersey in order to train civilian and military pilots.
The P-47C was sent to England for combat operations in late 1942. The 56th FG was sent overseas to join the 8th 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.
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.
P-47D / P-47G / XP-47K / XP-47L
Refinements of the Thunderbolt continued, leading to the P-47D, of which 12,602 were built. The ‘D’ model actually consisted of a series of evolving production blocks, the last of which were visibly different from the first.
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. gal (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:
* 200 U.S. gallon (758 l) ferry tank, a conformal tub-shaped jettisonable tank made of paper, which barely cleared the ground on grass airfields, was used as an interim measure between 30 July and 31 August 1943;
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 ft (3.96 m) and the Long Island plant using a Hamilton Standard propeller with a diameter of 13 ft 2 in (4.01 m). With the bigger propellers having barely 6 in ( mm) 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 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. gal (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 in (127 mm) High velocity aircraft 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.
XP-47H / XP-47J
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 hp (2,090 kW), reduced armament of six 0.50 in (12.7 mm) machine guns, a new and lighter wing, and many other changes. The 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 505 mph (440 kn, 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-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 USAF and ANG inventories.
The type was provided to many Latin American air forces some of which operated it into the 1960s. Small numbers of P-47s were also provided to China, Iran, Turkey and Yugoslavia.
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.
Flying the Thunderbolt
The turbosupercharger in the P-47 gave the powerplant its maximum power at 27,000 ft (8,230 m), and in the thin air above 30,000 ft (9,144 m), the Thunderbolt became comparatively fast and nimble relative to other aircraft.
One early P-47 squadron, the 4th Fighter Group, was composed mainly of pilots who had previously flown the British Supermarine Spitfire, and were not complimentary to their new plane. One Thunderbolt pilot compared it to flying a bathtub around the sky. When his unit (4th Fighter Group) was equipped with Thunderbolts, ace Don Blakeslee said, referring to the P-47's vaunted ability to dive on its prey, ‘It ought to be able to dive. It certainly can't climb.’ (Blakeslee's early-model P-47C had not been fitted with the new paddle-blade propeller). The 4th Fighter Group's commander hated the plane, and his prejudices filtered down to the group's pilots; the 4th had the fewest kills of any of the first three P-47 squadrons in Europe.
The P-47's initial success in combat was primarily due to tactics, using rolls (the P-47 had an excellent roll rate) and energy-saving dive and zoom climbs from high altitude to outmaneuver German fighters. No German piston-engined plane could out-dive the Thunderbolt. The Thunderbolt was the fastest-diving American aircraft of the war — it could reach speeds of 550 mph (480 kn, 885 km/h). Major Robert S. ‘Bob’ Johnson described the experience of diving the big fighter by writing, ‘the Thunderbolt howled and ran for the earth’. Some P-47 pilots claimed to have broken the sound barrier, but later research revealed that due to the pressure buildup inside the pitot tube at high speeds, airspeed readings became unpredictably exaggerated.
The arrival of the new Curtiss paddle-blade propeller significantly increased climb rate at lower altitudes, and came as a shock to German pilots who had resorted to steep climbs to evade pursuit by the P-47. Other positive attributes included the P-47's ruggedness; it could sustain a large amount of damage and still be able to get its pilot back to base. With eight .50 in (12.7 mm) machine guns, the P-47 did not lack for firepower. German aircraft caught in a well-aimed burst tended to fly apart from the impact of so many armor-piercing projectiles.
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, Thunderbolts 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. 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.
Ground attack role
The P-47 gradually became the USAAF's best fighter-bomber, normally carrying 500 lb (227 kg) bombs, M8 4.5 in (115 mm) or 5 in (127 mm) High velocity aircraft rockets (HVARs, or Holy Moses). 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.
The Thunderbolt's eight .50 in (12.7 mm) machine guns could inflict heavy damage on lightly armored targets. In a ground attack role, the .50 in (12.7 mm) armor-piercing (AP), armor-piercing incendiary (API), and armor-piercing incendiary tracer (APIT) ammunition proved useful in penetrating thin-skinned and lightly armored German vehicles and exploding their fuel tanks, as well as damaging some types of enemy armored fighting vehicles (AFVs). The dreaded cry of Achtung! Jabos! (fighter-bombers) regularly erupted from German armored columns as the P-47 flights got to work. While the AP projectiles from the .50 in (12.7 mm) machine guns could not penetrate the front, side, or turret armor of enemy tanks, it could sometimes penetrate the engine grilles and exhaust system of the German Pzkpf Mk IV or Pzkpf V (Panther), disabling the vehicle. The Mk IV had 10-12 mm top and bottom hull armor and the Panther had top and bottom hull armor made of 16 mm thick plate, while the .50 in (12.7 mm) AP/API round could completely perforate ⅞in (22 mm) face-hardened steel plate at 300 ft (91 m) and ¾ in (19 mm) at 1,640 ft (500 m). Additionally, .50 in (12.7 mm) bullets fired against German medium tanks traveling on paved roads tended to ricochet upwards, hitting the tank on its thinly-armored underside, sometimes richoceting inside the crew compartment or penetrating the engine compartment and setting the vehicle ablaze. The .50 in (12.7 mm) guns were ineffective against heavy German tanks such as the Tiger, which required the use of 500 lb bombs or 4.5 in (115 mm) or 5 in (127 mm) rockets.
For heavily-armored targets, P-47 pilots frequently carried two 500 lb (227 kg) bombs, using skip bombing techniques for difficult targets (skipping bombs into railroad tunnels to destroy hidden enemy locomotives or tanks was a favorite tactic); Tunnel-busting became a fine art. When pilots spotted a train entering a tunnel, they skipped bombs into both ends to seal the train inside, then bombed the tunnel itself. Near Canisy, France, a locomotive was shredded until it looked like a steel broom. A near miss was sufficient to knock a tank on its side, blow off a track or turret, or cause serious damage to tracks, suspension, and turret mechanisms, frequently causing the vehicle to be abandoned by its crew. The adoption of the triple-tube rocket launcher with M8 high-explosive 4.5 in (110 mm) rockets (with an explosive force similar to a 105 mm artillery shell), significantly increased the P-47's ground attack capability. Late in the war, the P-47 was retrofitted with more powerful 5 in (130 mm) HVAR rockets.
P-47 in non-U.S. service
During the Italian campaign, the ‘1º Grupo de Caça da Força Aérea Brasilira’ (Brazilian Air Force 1st Fighter Squadron) flew a total of 48 P-47Ds in combat (of a total of 67 received, 19 of which were backup aircraft). This unit flew a total of 445 missions from November 1944 to May 1945 over northern Italy and Central Europe, with 15 P-47s lost to German flak and five pilots being killed in action. In the early 1980s, this unit was awarded the ‘Presidential Unit Citation’ by the American government in recognition for its achievements in World War II.
From March 1945 to the end of the war in the Pacific, the Mexican Escuadron Aereo de Pelea 201 (201st Fighter Squadron) operated P-47Ds as part of the U.S. 5th Air Force in the Philippines. In 791 sorties against Japanese forces, the 201st lost no pilots or aircraft to enemy action.
The French Air Force received 446 P-47Ds from 1943. These aircraft saw extensive action in France and Germany and again in the 1950s during the Algerian War of Independence.
After World War II, 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. However, they were not well liked, as the Italian pilots were used to much lighter aircraft and found the controls too heavy. Nevertheless, the stability, payload and high speed were appreciated. Most importantly, the P-47 served as an excellent transition platform 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 special-purpose ground-attack aircraft, the Ilyushin Il-2.
Specifications (P-47D Thunderbolt)
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