The Republic P-47 Thunderbolt was a World War II era fighter aircraft produced by the United States between 1941–1945. Its primary armament was eight .50-caliber machine guns, four per wing, and in the fighter-bomber ground-attack role it could carry five-inch rockets or a bomb load of 2,500 pounds, more than half the payload of the Boeing B-17 Flying Fortress bomber. When fully loaded the P-47 weighed up to eight tons making it one of the heaviest fighters of the war. The P-47 was designed around the powerful Pratt & Whitney R-2800 Double Wasp engine which was the same engine also used by two very successful U.S. Navy fighters, the Grumman F6F Hellcat and the Vought F4U Corsair. The Thunderbolt was very effective as a short-to-medium range escort fighter in high-altitude air-to-air combat but was also adept at ground attack in both the World War II European and Pacific Theaters.