Built in greater quantities than any other US fighter, the P-47 was the heaviest single-engine WWII fighter to go into production and the first piston-powered fighter to exceed 500 mph. The Thunderbolt performed 546,000 combat sorties between March of 1943 and August 1945 and is considered the real forerunner of today's multirole fighters.
The Republic P-47 was the successor of a line of airplanes derived from the Seversky P-35, the XP-41, P-43 Lancer and XP-44 Rocket. The P-47 design team headed by Alexander Kartveli, Republic Aircraft Corporations's chief engineer, originally presented a design that was to be powered by a 1,150 hp Allison V-1710-39 engine with an armament of only two 0.50 inch machine guns.1 A contract was awarded by the USAAC in November 1939, and for an even lighter XP-47A, but as intelligence was coming back from the war in Europe, it was becoming apparent that the performance goals of the XP-47 program were already inadequate. The USAAC issued new requirements which included:1. Airspeed of 400 mph at 25,000 feet.
2. Armament of six .50 caliber machine guns, preferably eight.
3. Armor plating to protect the pilot.
4. Self sealing fuel tanks.
5. A minimum of 315 gallons of fuel.
The USAAC notified Kartveli that the XP-47A and the XP-44 Rocket contracts were canceled, since P-43/XP-44 airframe was to small to meet the new requirements. (The XP-44 Rocket was based on the P-43 Lancer airframe with a radial engine and never made it past the mock-up stage.) Kartveli then quickly prepared a rough sketch of a new XP-47B prototype, but it was a daring concept. He planned to use the new 2,000 hp Pratt & Whitney Double Wasp XR-2800-21, eighteen cylinder, two-row radial engine, which was the largest and most powerful aircraft engine ever developed in the United States.2 The new design would incorporate eight 0.50 inch machine guns, additional ammunition, increased fuel capacity and armor protection for the pilot. (The final fuel load was slightly under the capacity required, but this was overlooked as the aircraft met performance specifications.) Additionally the airplane would include an efficient super-charging duct system that would offer the least interrupted airflow. Kartveli therefore adopted the unorthodox method of designing this feature first, and then building up the fuselage around it. Despite the fact that the supercharger was in the tail and the engine was in the nose, the arrangement worked quite well—providing a system that was durable and less susceptible to battle damage
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