The Republic P-47 Thunderbolt is one of the largest and heaviest fighter aircraft in history to be powered by a single 4 stroke internal combustion engine. It was built from 1941-1945. It was heavily armed with eight .50-caliber machine guns, four per wing. When fully loaded, the P-47 weighed up to eight tons, and in the fighter-bomber ground-attack roles could carry five-inch rockets or a significant bomb load of 2,500 pounds; it could carry more than half the payload of the B-17 bomber on long-range missions (although the B-17 had a far greater range). The P-47 was designed around the powerful Pratt & Whitney R-2800 Double Wasp engine-the same engine used by two very successful U.S. Navy fighters, the Grumman F6F Hellcat and Vought F4U Corsair, the latter aircraft itself the first to fly with Double Wasp power in late May 1940-and was to be very effective as a short-to-medium range escort fighter in high-altitude air-to-air combat. When deployed as a fighter-bomber with its usual "double quartet" of heavy-caliber M2 Browning machine guns, it proved especially adept at ground attack in both the World War II European and Pacific Theaters.