The Convair B-36 "Peacemaker"[N 1] was a strategic bomber built by Convair and operated solely by the United States Air Force (USAF) from 1949 to 1959. The B-36 was the largest mass-produced piston engine aircraft ever made. It had the longest wingspan of any combat aircraft ever built at 230 ft (70.1 m). The B-36 was the first bomber capable of delivering any of the nuclear weapons in the U.S. arsenal from inside its four bomb bays without aircraft modifications. With a range of 10,000 mi (16,000 km) and a maximum payload of 87,200 lb (39,600 kg), the B-36 was the world's first manned bomber with an unrefueled intercontinental range. The B-36 was the primary nuclear weapons delivery vehicle of the Strategic Air Command (SAC) until it was replaced by the jet powered Boeing B-52 Stratofortress (which first became operational in 1955). The B-36 set the standard for range and payload for subsequent U.S. intercontinental bombers.