There were ten Thunderbolt groups with the Eighth Air Force by the end of 1943, but since the P-51 promised better range, the P-47 was then directed into the Ninth Air Force, where its firepower could be used for ground attack. By June 1944, 17 P-47D groups were stationed in the United Kingdom.
In the Pacific, the Fifth Air Force got three P-47D groups, beginning with the arrival of the 348th at Port Moresby in June 1943. More Thunderbolts replaced the 35th Group’s P-39s and the 58th Group arrived in November. The 49th Group operated one squadron each of P-38, P-40, and P-47 fighters in 1944. The 318th Group in Hawaii got 71 P-47D-21s that entered combat at Saipan after being flown off two escort carriers in June 1944.
Thunderbolts also re-equipped the 33rd and 81st Groups when they were sent to China in 1944, and in India they served the 1st Air Commando Group. In the Mediterranean, the P-47 replaced the 57th and 325th Groups’ P-40s in December 1943, and P-47Ds were flown by five more Twelfth Air Force combat groups in Italy during 1944.
A laminar-flow wing with straight trailing edges, 42-foot span, and 322-square foot area replaced the elliptical Republic S-3 airfoil on the 44th airframe by June 25, 1942. This XP-47F was flown in July and delivered to Wright Field September 17, 1942. Its 421-mph top speed did not justify more development.
The only pencil-nosed Thunderbolt was the XP-47H, a flying test bed for an experimental Chrysler 16-cylinder XIV-2220 inverted inline engine. Although the project was begun in August 1943, the two P-47D-15-RA airframes were not converted until 1945. Test flights began July 26, 1945, but speed fell below the 490 mph expected and jet propulsion killed official interest in the Chrysler power plant.
By November 1942, an XP-47J project was planned to reduce Thunderbolt weight and explore the speed limits of propeller-driven aircraft. Powered by an R-2800-57 giving 2,800-hp war emergency power, this type had a fan behind the prop spinner to suck cooling air over the cylinders, exhaust ejection to boost speed, and lightweight wing construction with ordnance reduced to six .50-caliber guns and 1,602 rounds. The contract was approved July 18, 1943, and the XP-47J first flew November 26.
A proposal to use counter-rotating propellers with an R-2800-61 on production P-47Js had been dropped in August 1943 in favor of P-72 development. On an August 5, 1944, test, the XP-47J did 505 mph, fastest speed for a propeller-driven aircraft officially announced during the war.
The next Thunderbolt models tested features more readily put on production aircraft. A bubble canopy was introduced on the XP-47K, completed July 3, 1943, from the last D-5, and on the XP-47L, which was the last D-20 with internal fuel capacity increased from 305 to 370 gallons.
Visibility with this cockpit cover, copied from the Hawker Tempest, was so improved that production lines in both factories changed over from the old “razor-back” shape to the bubble canopy and larger tanks with the P-47-25-RE first delivered on February 3, 1944. The first 2,963 P-47D to P-47D-22-RE produced by April at Farmingdale had the old style cockpit while the last 2,546, with block numbers from P-47D-25 on, had the bubble canopy. At Evansville, the first 2,350 P-47D to P-47D-23-RA were old style; the last 3,743 (Blocks D-26 to 40) were new.
Characteristics of the P-47D-25 are typical of the line. Fuel load could include up to 370 gallons internally plus 330 in drop tanks, which could extend the radius of action to 690 miles for fighter sweeps. Radius with one 165-gallon drop tank and one 1,000-pound. bomb was 518 miles; with two 1,000-pound bombs, 320 miles. In this latter role, as a low-altitude fighter bomber, the heavily-armed Thunderbolt was outstanding through the last year of the European war. Dive recovery flaps appeared on the D-30 block along with rails for ten five-inch rockets. A dorsal fin extension was added in service, and on the P-47D-40-RA at the factory.
The new Thunderbolts went to the Ninth Air Force, which had 13 P-47D groups for the D-Day landing in France and 14 groups at VE Day. These Thunderbolts’ attacks ahead of the Allied armies advancing into Germany helped cripple enemy resistance in the war’s last stage.