It *did* start as a lightweight interceptor..
Here's a write-up I wrote last year...
The History of the Republic P-47 Thunderbolt.
The development of the P-47 started in 1935. The Army was looking for a replacement of the Boing P-26 and 2 Russian born emigrants, Alexander Severski and Alexander Kartveli attracted the Army's interested with the SEV-1XP, renamed the P-35. Their main contender was Curtiss with their P-36, but in June 1936 Severski & Kartveli was awarded the contract of 76 P-35's.
In 1939, While Severski was in England to promote his ideas, but back home he was voted out of the board of directors and had to accept a cash settlement for his position. He used those money to from a new company in October 1939, called the Republic Aviation Corporation and with him took Kartveli as his chief engineer.
Again the Army was looking for a new fighter and with new technology, ever increasing poweful engines were becoming available, although their reliability were mainly unproven.
Initially Kartveli was aimin for a lightweight interceptor with as small an airframe as possible, using the new V-12 liquid-cooled Allison engine. The first design, named the AP-10 recieved a positive reception by the Army Board in August 1939 and Kartveli was asked to develop it.
The original weight was 4600lbs, but as the army wanted provisions for bomb racks and other modifications, the weight rose to 4900lbs with 2 fuselage mounted machine guns.
Initial performance estimates was 415mph at 15,000 feet and the plane was renamed the XP-47, but as the technology went further, the original design was deemed outdated and in January 1940 they agreed on re-designing it.
Meanwhile, with air war in Europe highlighted several subjects and the army started to demand new features like armour plating & self-sealing fuel tanks. The Army Board also expressed concern about the Allison engine, but Kartveli had foreseen this by turning his attention on the Pratt & Whitney Double Wasp.
Due to the massive size of the Double Wasp, Kartveli created a new airframe and the Republic submitted their new design, the XP-47B. The Army Board was quite encouraged with the armament of 6 0.50-in Browning machineguns, an estimated topspeed of 400mph at 20,000 feet and a climbrate of 5 minutes to 15,000 feet. The weight had now grown to 11,600 lbs, the biggest ever single seat fighter.
On the 6th of September 1940, the Army Air Corp issued a contract of 773 P-47B's.
To get the promised performance of the Double Wasp, Kartveli decided to install a supercharger. Only problem was that it took up a lot of space, but by installing the main part of the unit in the rear fuselage, behind the pilot, he solved the problem.
The first prototype, XP-47B (serial no. 40-3051), had looked nothing like the biplanes still used around the world and was for it's time, extremly futuristic with it's polished aluminium airframe, elliptical wings and closed canopy. It featured the Curtiss Electric propeller, the first 4 bladed propeller to be fitted a US plane, the P&W Double Wasp, a 18 cylinder radial engine outputting a massive 2000hp and a fuel capacity of 305 gallons. From the P-35s 28 feet & 4600lbs, it had grown to more than 35 feet and a loaded weight of 12,500 lbs, the largest single seat fighter ever!.
On the 6th of May, 1941, test pilot Lowery Brabham rolled the XP-47B down the runway at Farmingdale and the P-47 flew for the first time. Although smoke started to pour into the cockpit, Brabham flew for 20 minutes and due to the soft runway at Farmingdale from recent rain,diverted and landed succesfully at the nearby Mitchell Field. After several test flights, it gained a topspeed of 412 mph at 25,800 feet, fulfilling the promise of a topspeed over 400 mph and production of the first series of P-47B's started.
A series of setbacks then followed. On the 26th of March 1942, chief test pilot George Burrell was killed during a test flight when the entire tail section broke away. On the 1st of May another P-47 was damaged in a high speed dive, but managed to land with most of the fabric covered rudder and elevator in shreds.
The Republic strenghtened the airframe and fitted metal covered control surfaces, but as with other plane designs, the high-speed problems were only partially solved.
In October 1942, 3 P-47C-1's were delivered to Army Air Force for combat evaluation test. An impressive topspeed of 427 mph was recorded, but the rate of climb was somewhat disappointing with 7 minutes to 15.000, not exactly what you expect from a interceptor fighter.
It was the Republics Director for Military Contracts, C. Hart Miller who named it "Thunderbolt".
15,683 Thunderbolts were built during the war, more than any other allied fighter and it recorded 3,916 enemy plane kills, 6,000 tanks, 9,000 locomotives, 86,000 rail wagons and 68,000 trucks.
Daff
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CO, 56th Fighter Group
