The P-47D was the first version of the Thunderbolt to undergo really large-scale production. The first USAAF order for the P-47D took place on October 14, 1941, when 850 examples were ordered. However, it was to be followed by many, many more.
In its initial form, the P-47D differed very little from the P-47C-5-RE which preceded it on the Farmingdale production lines. The P-47D had some changes in the turbosupercharger exhaust system which incorporated an adjustable duct and redesigned vents for the engine accessory section. Additional cowl flaps were fitted to prove engine cooling airflow. More extensive armor protection was provided for the pilot. Generally, however, early P-47Ds can be distinguished from Cs only by their serial numbers.
Demand for the Thunderbolt was so great that Republic built a new factory at Evansville, Indiana to augment production of the P-47D. 1050 P-47Ds were ordered from Evansville on January 31, 1942, and the first Evansville-built P-47D (serial number 42-22250) rolled off the assembly line in September of 1942. Evansville-built P-47Ds were distinguished from Farmingdale-built P-47Ds by the use of the RA manufacturer letter code rather than RE. They could be distinguished from Farmingdale-built P-47Ds only by their serial numbers.
Following cancellation of the Army contract for the P-60A in January 1942, the Curtiss-Wright company was given a contract to begin construction of the D-version of the Thunderbolt under license at its Buffalo plant. The Curtiss-Wright built version was designated P-47G. The first delivery of a P-47G took place in December of 1942. The first 20 P-47Gs produced by Curtiss (P-47G-CU) were similar to the concurrent P-47C, but the remainder were similar to Republic-built P-47Ds. Curtiss produced a total of 354 P-47G-1-CU through P-47G-15-CU Thunderbolts by March of 1944, these planes being identical to Republic-built P-47Ds. They could be distinguished from Republic-built Thunderbolts only by their serial numbers. Since P-47Gs tended to lag behind Republic-built models as regards the latest refinements, most of the Curtiss-built Thunderbolts were used for training roles in the US, and very few went overseas. Curtiss production ended in March of 1944
All early Thunderbolts used the R-2800-21 engine. Water injection capability was added to this engine beginning with the D-4-RA and D-5-RE production blocks. Provision was made for the mounting of 15-gallon tank carrying a water-alcohol mixture to the bulkhead just aft of the engine. A line from this tank was plumbed directly into the fuel intake. When injected into the combustion chamber, the water checked a dangerous rise in cylinder head temperature while manifold pressure was boosted. For brief instants, a 15-percent increase in engine power could be obtained, giving a maximum war emergency power of 2300 hp. In the D-5-RE, D-6-RE, and D-10-RE (D-4-RA, production bolcks, the pilot manually controlled the water flow of the injector, but the injection procedure was automatically- controlled on the D-11-RE (D-11-RA) and subsequent blocks. This happened when the throttle was pushed forward into its last half-inch of travel.
When installed at the factory, the water-injected engines were designated R-2800-63. The R-2800-63 engine began to appear on the Farmingdale and Evansville production lines with blocks D-10-RE and D-11-RA respectively. Kits were also made available for the retro- fitting of water injection capability to earlier P-47Cs and Ds. Since they were already built to accommodate water-injection, the D-4, -5, and -6 could be quickly modified, but the D-1, -2, and -3 and the earlier C-2 and C-5 each requireed about 200 hours of work for each addition of water-injection capability.
Shackles for a belly tank or a 500-pound bomb were added to P-47D-5-RE (D-11-RA) and later blocks.
Underwing pylons were introduced on the D-15-RE and D-15-RA production blocks. These enabled a drop tank or a bomb to be carried underneath each wing in addition to the stores carried on the belly shackles. Fuel changes had to be made to incorporate plumbing for the underwing tanks. Bomb selection increased to two 1000-pound or 3 500-pound bombs, with maximum bombload being 2500 pounds. Alternatively, a 108-gallon drop tank could be carried underneath each wing, adding 150 miles to the P-47's range. Earlier P-47C and D models could be modified in the field to accommodate underwing racks, but the amount of work required many man-hours of effort by maintenance personnel. The underwing pylons had a detrimental affect on performance, and their air resistance cut 45 mph off the maximum speed. However, a redesigned, more streamlined pylon cut the loss to about 15 mph.
Two Curtiss-built P-47Gs were converted as tandem, two-seat trainers. One of the fuselage fuel tanks was removed and a second cockpit was fitted in its place. Known as the TP-47G, these aircraft retained the eight-gun armament of the single-seat version.
Toward the end of 1943, Eighth Air Force Thunderbolts began returning from escort missions over the Continent "on the deck", seeking out enemy ground targets of opportunity for their unused ammunition as they made their way back to the Channel. Somewhat surprisingly, it was found that the Thunderbolt was rather well-suited for this new role. This led to perhaps the most successful adaptation of the Thunderbolt--as a fighter-bomber.
The P-47D-6-RE to P-47D-11-RE and P-47G-10-CU to 15-CU production blocks had only ventral shackles, which were stressed to accommodate one 500-lb bomb, but subsequent production blocks were fitted with underwing pylons and stronger wings which permitted them to carry two 1000-lb bombs, three 500-lb bombs or a combination of bombs and drop tanks. Either six or eight machine guns could be carried, and maximum ammunition capacity was 425 rpg. However with the full ordinance load, ammunition capacity was reduced to 267 rpg.
At about this time, a number of Thunderbolts suffered mysterious engine failures during missions over the Continent that could not be ascribed to enemy action. It was eventually discovered that the additional weight of the bombs and drop-tanks added so much weight to the aircraft that the Thunderbolt was able to build up excessively-high speeds during bombing attacks. During the recovery from these high-speed dives, g-forces got so high that a surge or vapor lock was produced in the fuel lines which the fuel pump was unable to overcome.
Production batches from the P-47D-20-RE onward were fitted with a "universal" wing which could carry a variety of drop tanks or bombs. These batches also introduced the R-2800-59 engine with an improved ignition system. The power was the same as that of the -63, with a war emergency power output of 2300 hp. The length of the tail wheel leg was increased.
Beginning with production blocks D-22-RE and D-23-RA, a larger (13- foot diameter) paddle-bladed propeller (either a Hamilton Standard Hydromatic 24E50-65 or a Curtiss Electric C542S) was fitted to make full use of the additional power provided by water injection. It added 400 feet per minute to the climb rate, but during landings and takeoffs there was only a scant six inches of clearance between blade tips and the ground. Takeoffs and landings must have both been hair-raising.
Blocks D-22-RE and D-23-RA were also provided with a jettisonable cockpit canopy which was activated by the pilot pulling a ring. The hood would then be pushed backward, and the force of the slipstream would then do the rest of the job of pulling the canopy free of the aircraft. A bullet-proof windshield was fitted, and internal fuel capacity was increased.
The 3962 P-47D-1RE to -22-RE Farmingdale-built Thunderbolts, the 1461 P-47D-2-RA to -23-RA Evansville-built Thunderbolts, and the entire lot of 354 P-47G-1-CU through P-47G-15-CU Curtiss-built Thunderbolts all had the original framed sliding canopy that was first used on the P-47B. However, combat experience indicated that the the rear fuselage decking on these Thunderbolts provided a serious blind spot aft which was a real hindrance in air-to-air battles. In an attempt to improve rearward visibility, a few P-47Ds were fitted in the field with the RAF "Malcolm hood", a Spitfire-like bubble canopy made in England which was made famous by its application to the P-51B and C Mustangs flown by both the RAF and USAAF. However, P-47Ds fitted with Malcolm hoods were quite rare, whereas P-51Bs and Cs with Malcolm hoods were quite common.
In the meantime, in search of a more lasting solution the USAAF fitted a standard P-47D-5-RE airframe (serial number 42-8702) with a bubble canopy taken from a Hawker Typhoon. In order to accommodate the bubble canopy, the Republic design team had to cut down the rear fuselage. This conversion was redesignated XP-47K, and was tested in July 1943. This modification was immediately proven to be feasible, and was promptly introduced on both the Farmingdale and Evansville production lines.
Ordinarily, the USAAF would have given such a radical modification as that which produced the bubble-canopy Thunderbolt a completely new variant letter (or perhaps even a new type number). However, the USAAF chose instead to designate it simply by giving it a new production block number in the D-series. Consequently, the first batches to feature this new bubble canopy were Farmingdale's P-47D-25-RE and Evansville's P-47D-26-RA. These batches also had the R-2800-59 or -63 engines, the paddle-bladed propeller, and the "universal" wing first introduced on the "razor-back" P-47D-20-RE. Stronger belly shackles capable of carrying a 91.6 Imp. gall. drop tank were fitted. This tank, together with the 170.6 Imp. gall. main fuselage tank, an 83-gallon auxiliary fuel tank and two 125-gallon underwing tanks, made it possible to carry a total fuel load of 595 Imp. gall, providing a maximum range of 1800 miles at 195 mph at 10,000 feet.
A single P-47D-20-RE (serial number 42-76614) was taken off the production line and modified as XP-47L with a bubble canopy as in the XP-47K and with increased capacity fuel tanks which raised internal fuel capacity from 305 to 370 US gallons. Both of these changes were incorporated in the P-47D-25-RE production batch.
The early "bubble-canopy" Thunderbolts had suffered from some directional instability as a result of the loss of aft keel area. From the P-47D-27-RE production lots onward, a dorsal fin was fitted just ahead of the rudder. This innovation successfully restored the stability.
Underwing zero-length launching stubs for a total of ten five-inch HVAR rockets were fitted to Thunderbolts from production blocks P-47D-30-RA onward.
The high diving speeds of which the Thunderbolt was capable pushed the aircraft into the edge of compressibility, and new blunt-nosed ailerons were fitted to improve controllability at these high speeds. In order to help in dive recovery at these high speeds, an electrically-operated dive recovery flap was fitted on the undersurfaces of each wing.
Farmingdale produced a total of 2547 bubble-canopy P-47Ds and Evansville built 4632. the Japanese.
During the immediate postwar years, numerous surplus ex-USAAF Thunderbolts were supplied to foreign air forces. These included the air forces of Bolivia, Brazil, Chile, China, Colombia, Dominica, Ecuador, Honduras, Iran, Nicaragua, Peru, Turkey, Venezuela, and Yugoslavia. Some of these foreign-operated Thunderbolts remained flying until the late 1960s until they were finally replaced by jet aircraft.
A "razorback" P-47D is on display at the Champlin Fighter Museum at Mesa, Arizona. A Thunderbolt is also on display at the WPAFB museum, but I don't have any record of its serial number.
Specifications of the P-47D-25-RE:
One Pratt and Whitney R-2800-59 Double Wasp eighteen-cylinder air-cooled radial, war emergency power of 2535 hp. Maximum speed was 429 mph at 30,000 feet, 406 mph at 20,000 feet, 375 mph at 10,000 feet, 350 mph at sea level. Initial climb rate was 2780 feet per minute. Climb rate at 30,000 feet was 1575 feet per minute. Service ceiling was 40,000 feet, and range was 950 miles at 10,000 feet. Range with maximum external fuel was 1800 miles at 10,000 feet at 195 mph. Weights were 10,700 pounds empty, 14,600 pounds normal loaded, and 17,500 pounds maximum. Dimensions were wingspan 40 feet 9 3/8 inches, length 36 feet 1 3/4 inches, height 14 feet 7 inches, and wing area 300 square feet.
Serials of Republic Farmingdale-built P-47Ds:
42-7853/7957 Republic P-47D-1-RE Thunderbolt 42-7958/8402 Republic P-47D-2-RE Thunderbolt 42-8403/8702 Republic P-47D-5-RE Thunderbolt 42-25274/25322 Republic P-47D-20-RE Thunderbolt 42-25323/25538 Republic P-47D-21-RE Thunderbolt 42-25539/26388 Republic P-47D-22-RE Thunderbolt 42-26389/26773 Republic P-47D-25-RE Thunderbolt 42-26774/27388 Republic P-47D-27-RE Thunderbolt 42-74615/74964 Republic P-47D-6-RE Thunderbolt 42-74965/75214 Republic P-47D-10-RE Thunderbolt 42-75215/75614 Republic P-47D-11-RE Thunderbolt 42-75615/75814 Republic P-47D-15-RE Thunderbolt 42-75865/76118 Republic P-47D-16-RE Thunderbolt 42-76119/76364 Republic P-47D-15-RE Thunderbolt 42-76365/76614 Republic P-47D-20-RE Thunderbolt 44-19558/20307 Republic P-47D-28-RE Thunderbolt 44-20308/21107 Republic P-47D-30-RE Thunderbolt Serials of Republic-Evansville built P-47Ds 42-27389/28188 Republic P-47D-23-RA Thunderbolt 42-28189/28438 Republic P-47D-26-RA Thunderbolt 42-28439/29466 Republic P-47D-28-RA Thunderbolt 42-22250/22363 Republic P-47D-1-RA Thunderbolt 42-22364/22563 Republic P-47D-2-RA Thunderbolt 42-22564/22663 Republic P-47D-3-RA Thunderbolt 42-22664/22863 Republic P-47D-4-RA Thunderbolt 42-22864/23113 Republic P-47D-11-RA Thunderbolt 42-23114/23142 Republic P-47D-16-RA Thunderbolt 42-23143/23299 Republic P-47D-15-RA Thunderbolt 43-25254/25440 Republic P-47D-20-RA Thunderbolt 43-25441/25664 Republic P-47D-21-RA Thunderbolt 43-25665/25753 Republic P-47D-23-RA Thunderbolt 44-32668/33867 Republic P-47D-30-RA Thunderbolt 44-89684/90283 Republic P-47D-30-RA Thunderbolt 44-90284/90483 Republic P-47D-40-RA Thunderbolt 45-49090/49554 Republic P-47D-40-RA Thunderbolt Serials of Curtiss-built P-47Gs: 42-24920/24939 Curtiss P-47G-CU Thunderbolt 42-24940/24979 Curtiss P-47G-1-CU Thunderbolt 42-24980/25039 Curtiss P-47G-5-CU Thunderbolt 42-25040/25119 Curtiss P-47G-10-CU Thunderbolt 42-25120/25273 Curtiss P-47G-15-CU Thunderbolt