Republic Thunderbolt

The Republic P-47 Thunderbolt really should have been designed and built in Texas, for it was the biggest and heaviest fighter ever to have served with the USAAF when it entered service in 1942; it also belonged to the select, small number of aircraft to be designed, developed, produced and used in action during World War II. It was one of an even more select group, being among the trio of great USAAF fighter aircraft created by the US aviation industry to take part in that war.

And with regard to the foregoing, it is perhaps a little ironic to discover that the P-47 was originated to meet a US Army Air Corps requirement of 1940 for a lightweight interceptor. Its family tree, of course, was clearly defined, from Alexander Seversky's P-35, via the XP-41, P-43 and P-44. The P-35 had been evolved from an earlier Seversky design by the genius of Alexander Kartveli, and it was the design team headed by this man that produced the P-47.

In 1939 the team began development of a new fighter, of lightweight construction, powered by a 1,150 hp (858 kW) Allison V-1710-39 inline engine, and with armament of only two 12.7 mm (0.50 in) machine-guns. A prototype contract for this XP-47 was awarded by the USAAC in November 1939, as was a contract for an even lighter-weight variant designated XP-47A. But with the receipt in early 1940 of information on air combat in Europe, it was immediately clear that neither of these projects was likely to mature into a fighter aircraft that would have any reasonable chance of survival in European skies. The XP-47/-47A prototypes were cancelled, for not even by wearing the rosiest of 'rose-coloured' spectacles could Republic or the USAAC envisage either of the prototypes proving suitable to incorporate the heavy armour, eight-gun firepower and self-sealing fuel tanks that appeared to be the minimum premium for a World War II survival policy.

Kartveli immediately outlined his proposals for a fighter that would meet the requirements, basing it on the use of a turbocharged Pratt & Whitney P,-2800 Double Wasp that would have sufficient power to lift a heavy load of arms, ammunition, armour and fuel, and still have something left over to give high performance. Evaluation of the design by the USAAC resulted in a contract for an XP-47B prototype being awarded on 6 September 1940, and this time the question of weight was ignored. From the design point of view this eliminated a major problem, for whilst it was obviously desirable to arrive at the lightest possible structure to provide integrity for the whole machine, it meant that any really worthwhile feature needed no longer be subordinated to weight saving.

The heart of the machine, of course, was its powerplant, comprising a 2,000 hp (1491 kW) R-2800 Double Wasp engine and its turbocharger. The aircraft was designed around the best possible installation of these two major assemblies, with the aim of having the most direct ducting between them so that ambient air, exhaust gases and pressure air would not be in any way restricted by cramped ducting. This put the turbocharger in the aft fuselage, the low wing being mounted a slight distance up from the base of the fuselage so that the main air ducting could pass straight beneath the wing spars. To convert this abundant horsepower into tractive effort a four-blade constant-speed propeller 12 ft 2 in (3.71 m) in diameter was necessary, but to provide adequate ground clearance for the propeller tips a taller than average landing gear was needed. These main units, retracting inward, were then too long for the space available in the wing between the inboard machine-gun and wing root, and the solution of this was a specially designed oleo-pneumatic strut that shortened as it retracted.

The rest of the structure was conventional all-metal (the prototype had fabric-covered control surfaces), but on a large scale, and when rolled out for the first time the new aircraft appeared to be nothing short of gigantic for a fighter. However, the first flight, on 6 May 1941, gave a hint of the aircraft's potential, but there were a number of problems to be resolved. Fortunately most of these had been cleared before the XP-47B crashed on 8 August 1942. This occurred before the flight test programme had been completed, but there was no significant hold up on the production which had already got under way to meet the initial contracts, for 773 aircraft, which had been placed very shortly after that for the prototype.

Production P-47Bs, which were given the name Thunderbolt, began to come off the line in March 1942, and in June began to equip the squadrons of the USAAF's 56th Fighter Group. The P-47B differed in only minor respects from the prototype: fabric-covered control surfaces replaced by all-metal structures, and the cockpit canopy aft-sliding instead of side-hinged, and the powerplant having an R-2800-21 production engine. By January 1943 the 56th Fighter Group had joined the 8th Air Force in Britain, soon after reinforced by the 78th Fighter Group, and these groups began operational sorties during April 1943. Initial encounters with the German fighters showed that the Thunderbolt was lacking in performance and manoeuvrability at low and medium altitudes, and also that range was inadequate, limited as it was by the amount of internal fuel that could he carried.

Production of the P-47B totalled 171, the last off the line being modified by the introduction of a pressurised cockpit under the designation XP-47E. The P-47Cs which followed, from September 1942, were basically similar to the P-47B except for a fuselage extension of 10 1/2 inches (27 cm) and changes in the rudder and elevator balance system to improve manoeuvrability. The powerplant was unchanged for early production aircraft, but the engine model introduced later had a water injection system to provide a combat rating of 2,300 hp (1715 kW) at 27,000 ft (8230 m). The most important change in relation to the tactical use of the Thunderbolt was the provision of attachment points for one 200 US gallon (757 litre) drop tank, and from July 1943 P-47Cs could be used deep into German airspace.

A total of 602 P-47Cs had been built before production switched to the most extensively built version, the P- 47D. The large numbers of Thunderbolts contracted were far beyond the productive capacity of Republic's Farmingdale, Long Island, factory so the company established a new production line at Evansville, Indiana, and arranged with Curtiss-Wright to begin production at Buffalo, New York. Between them these lines produced no fewer than 12,956 aircraft comprising 6,509 at Farrningdale (3,962 low and 2,547 high block numbers); 6,093 at Evansville (1,461 low and 4,632 high block numbers); and Curtiss-Wright built 354 to P-47D standard under the designation P-47G.

P-47Ds in the early block numbers varied only slightly from the previous production version, introducing more extensive armour protection for the pilot, slight improvements in the turbocharger exhaust system, and a water injection system as standard for both the R-2800-21 and -59 engines. However, improvements were incorporated throughout the entire production programme, and these included wing strengthening, the provision of underwing pylons to carry additional weapons or fuel and, on the high block numbers, one important change was ma e to improve rear vision, hitherto restricted by the rear fuselage decking. One P-47D was taken from the line and modified to reduce the height of the rear fuselage, and to replace the framed aft-sliding cockpit canopy by an all-round vision bubble canopy as used on the Hawker Typhoon. Designated XP-47K, this aircraft was tested extensively in July 1943, the improved visibility being acclaimed by all the pilots who flew it, and resulting in immediate adoption of the modification on production aircraft. At a slightly later stage a small dorsal fin was added to P-47Ds to offset the loss of keel surface which resulted from this change in configuration. Other changes in the later production aircraft included the introduction of the R-2800-63 engine and a paddle- blade propeller, and provision for a total internal plus external fuel capacity of 715 US gallons (2706 litres) to provide a maximum range of 1,800 miles (2897 km) under optimum conditions.

The US Sth Air Force began to receive its first P- 47Ds towards the end of 1943, and the variant later began to equip units of the 8th and 15th Air Forces in Europe. The 348th Fighter Group in Australia was the first to introduce the type in the Pacific theatre when it received its first aircraft late in 1943. The P-47D was also the first version of the Thunderbolt to be supplied under Lend-Lease, the RAF receiving 240 from the low block numbers with the original framed sliding cockpit canopy, and 585 from the high block numbers with the bubble canopy, under the designations Thunderbolt 1 and Thunderbolt 11 respectively. All were ' used to equip RAF squadrons operating in Burma, the first to receive these aircraft being No. 5. Other squadrons to be equipped included Nos. 30, 34, 42, 60, 79, 81, 113, 123, 131, 134, 135, 146, 258, 261 and 615. They proved to be a most valuable aircraft as deployed there in a fighter-bomber role, using the 'cab-rank' technique in which patrolling aircraft could be called in by ground controllers to blast Japanese troops with which they were in contact. The armament of up to three 500 Ibs (227 kg) bombs and the concentrated firepower of their eight machine-guns, combined with high performance at low level, represented a potent weapon against which the Japanese troops had little chance of retaliation. Other nations to be supplied with P-47Ds included Brazil (88), which had one squadron operating with the 12th Air Force in Italy in late 1944; the Free French forces (446); Mexico (25) to equip the 201st Fighter Squadron of the Mexican air force; and the USSP, (203).

A small run of P-47Ms followed the -47D on the production line, but it is desirable before discussing this to account for the designation gaps. The XP-47E with pressurised cockpit has been mentioned above, as has the P-47G which was the designation of the Curtiss-built P-47D; one P-47B was used to test the installation of laminar-flow wings as the XP-47F; and the XP-47H designation covered two P-47Ds in which new 2,300 hp (1715 kW) Chrysler XIV-2220-1 inline engines were installed to give higher performance, overall length being increased by 3 ft 0 1/4 in (0.92 m) in comparison with the P-47D. This version did not materialise in production form, however, as the Chrysler engine was not put into production. Far more radical was the XP-47J (no use was made of an I designation) which introduced a closely-cowled fan-cooled R-2800-61 engine rated at 2,100 hp (1 566 kW), and provided with a wing of lighter weight which incorporated six 12.7 mm (0.50 in) machine-guns. First flown on 26 November 1943, this experimental aircraft was the first piston-engined machine to exceed a speed of 500 mph (805 km/h) in level flight, attaining 504 mph (811 km/h) on 4 August 1944, but despite this sparkling performance production plans were abandoned in favour of an even more advanced project designated XP-72. The XP-47K has been mentioned above, and the XP-47L resulted from structural changes in a P-47D to provide greater internal fuel capacity.

The P-47M, of which only 130 were built, was preceded by three YP-47Ms. These introduced a similar combination of R-2800 engine and turbocharger as those which had proved so successful in the XP-47J, the engine being able to develop a combat rating of 2,800 hp (2088 kW) at 32,500 ft (9905 m). The aim was to produce a high-speed version of the P-47D airframe which could be put into operation quickly to counter the turbine and rocket-powered fighters in service with the Luftwaffe in Europe, as well as the V-1 flying bombs. which were very vulnerable to a high-speed fighter. Most of these aircraft served after D-Day with USAAF units in Europe, operating initially from Normandy.

Last of this famous line of fighters was the P-47N, of which 1,816 were produced, making the grand total of 15,677 Thunderbolts when production ended soon after VJ-Day. The P-47N utilised the powerplant which had proved so successful in the P-47M, the basic P-47D airframe with an enlarged dorsal fin, strengthened landing gear, and a new strengthened wing of increased span which, for the first time in any version of the P-47, included wing fuel tanks. The resulting maximum internal plus external fuel capacity of 1,146 US gallons (4338 litres) was sufficient to ensure that the P-47Ns deployed in the Pacific were able to provide an adequate escort service for XXI Bomber Command (VH) Boeing B-29 Superfortresses during long over-water missions.

This enormous fighter, a true juggernaut, indeed the 'Jug' to its friends, proved itself to be robust and reliable, able to absorb an enormous amount of punishment before being beaten by an enemy, and resulting in the exceptionally low loss rate for this type of 0.7 per cent. The P-47D and P-47N remained in USAF service for a number of years after the war, passing to Air National Guard units before being phased out of service in 1955, by which time they had been redesignated F-47D and F-47N respectively.

Even then, however, Thunderbolts had many more useful years of service to offer, operating with the air forces of Bolivia, Brazil, Chile, Colombia, Dominica, Ecuador, France, Guatemala, Honduras, Iran, Italy, Mexico, Nationalist China, Peru, Turkey and Yugoslavia.

Most famous of all Republic aircraft, the Republic P-47 Thunderbolt de- signed by Alexander Kartveli had a significant role to play in World War 11, and was built to an astonishing total of 15,677 before production came to an end with cancellation of outstanding contracts after VJ-Day. Like many other major combat aircraft, the P-47 acquired two nicknames bestowed affectionately by its pilots to a friend that had been tried and trusted in battle: 'Jug', a diminutive of Juggernaut that described its ample proportions, and 'T-bolt' derived from its officially-given name. A continuation of the family that had started with Alexander Seversky's P-35 and further developed through the P-43 Lancer and projected higher-performance P-44, the P-47 began by highlighting the indecision of the USAAC in 1940 about whether to procure lightweight or heavyweight fighters. Original plans to order the Republic AP-4 and AP-10 projects for lightweight fighters under the designations XP-47 and XP-47A respectively were cancelled when early re- ports of combat experience in Europe were received. Kartveli then outlined his proposals for a heavy fighter that would meet the new requirement, basing his concept on use of the turbocharged Pratt & Whitney R-2800 Double Wasp, and winning an order for an XP-47B prototype based on this design. A cantilever low wing monoplane, of conventional all-metal construction except for fabric- covered control surfaces, the new model had retractable taiiwheel landing gear and accommodated its pilot beneath an upward-hinged canopy.

When flown for the first time, on 6 May 1941, the XP-47B gave an immediate hint of the aircraft's potential, but there were a number of serious problems that had to be remedied. Orders from the US Army were soon received, initially for l7l production P-47B fighters, which began to come off the production line in March 1942 and to equip squadrons of the USAAF's 56th Fighter Group three rnonthsiater.ByJanuaryl943thisgroup had joined the 8th Air Force in the UK, shortly reinforced by the 78th Fighter Group, and these units became operational in April 1943. Initial encounters with German fighters showed that the Thunderbolt was lacking in performance and manoeuvrability at low and medium altitudes, and had inadequate range to operate as an escort fighter. These shortcomings were met by ensuing variants, which progressively increased the capability of this remarkable aircraft, then regarded as a giant or juggernaut but which, by today's standards, was really quite small. it was, nevertheless, a giant in achievement, robust, reliable and able to absorb an enormous amount of punishment from enemy weapons, with the exceptionally low loss rate of only 0.7 per cent per mission. The P-47 is credited with the destruction of 4.6 enemy aircraftf or the loss of each one of its own number, with some 546,000 combat sorties during which 1,934,000 operational flight hours were accumulated, and with the destruction in Europe (excluding the Italian front) of 3,752 enemy aircraft in the air and 3,315 on the ground. It is little wonder therefore that the P-47 is well remembered in the aviation history of World War 11.

In addition to service with the USAAF in the war, P-47s had been used also during this period by Brazil, the Free French air force, Mexico, the RAF, and the Soviet Union. The P-47D and P-47N remained in USAF service for a number of years after the war, passing to Air National Guard units before being phased out of service in 1954, by which time they had been redesignated F-47D and F-47N respectively. Even then, the Thunderbolt had many more years of useful service to offer, operating with the air forces of Bolivia, Brazil, Chile, Colombia, Dominica, Ecuador, France, Guatemala, Honduras, Iran, Italy, Mexico, Nationalist China, Peru, Turkey and Yugoslavia.   

Nicknames: Jug; T-Bolt

Specifications (P-47D):

Engine: 2535hp Pratt & Whitney R-2800-59W Double Wasp radial piston engine
Weight: Empty 9,950 lbs., Maximum Takeoff 17,500 lbs.
Wing Span: 40ft. 9.25in.
Length: 36ft. 1.75in.
Height: 14ft. 8in.

Maximum Speed: 433 mph
Ceiling: 41,000 ft.
Range: 1900 miles with drop tanks

Eight 12.7mm (0.5 in.) wing-mounted machine guns
Up to 2500 lbs. of externally-mounted bombs, rockets, or other free-fall ordinance

Number Built: 15,677

Number Still Airworthy: 9