Call the Mustang an American fighter if you like, but it was a success only with the Merlin engine. The Mustang was originally designed and built for the Brits- not for the Americans and it was a disappointment. It was rejected as a fighter for the USAAF and consideration was given to scrapping the program. It was only with the British Merlin engine that the Mustang was a successful fighter. It was great as a long range high altitude escort and dog fighter but it had a big weakness in the ground attack role. The water cooled engine was succeptable to ground fire where a single hit on the cooling system could bring down the plane.
The P-47 was superb in the ground attack role carrying a heavy load of ordinance. The plane could take a lot of punishment from ground fire on its air frame and air cooled radial engine. It had by far the best pilot mission surviveability rate. It was also a very effective dog fighter against Me109 and FW190.
"In Europe during the critical first three months of 1944 when the German aircraft industry and Berlin were heavily attacked, the P-47 shot down more German fighters than did the P-51 (570 out of 873), and shot down approximately 900 of the 1,983 claimed during the first six months of 1944. In Europe, Thunderbolts flew more sorties (423,435) than P-51s, P-38s and P-40s combined. Indeed, it was the P-47 which broke the back of the Luftwaffe in the critical period of January–May 1944"
The P-47 was so highly regarded with it's huge panels of shiny sheet metal, powerful engine and fins (wings and tail) that after the war it inspired the design of the Big metal and chrome, finned muscle cars of the 1950's and 1960's.
Terry