The Republic P-47 Thunderbolt was a World War II era fighter aircraft produced by the United States from 1941 through 1945. Its primary armament was eight .50-caliber machine guns and in the fighter-bomber ground-attack role it could carry five-inch rockets or a bomb load of 2,500 pounds (1,103 kg). When fully loaded the P-47 weighed up to eight tons (tonnes) 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 also used by two U.S. Navy fighters, the Grumman F6F Hellcat and the Vought F4U Corsair. The Thunderbolt was effective as a short-to-medium range escort fighter in high-altitude air-to-air combat and ground attack in both the World War II European and Pacific theaters.