The Northrop B-2 Spirit is an American heavy strategic bomber that uses low-observable stealth technology to penetrate sophisticated anti-aircraft defenses. It is often referred to as a stealth bomber.[3][A] A subsonic flying wing with a crew of two, the B-2 was designed by Northrop (later Northrop Grumman) as the prime contractor, with Boeing, Hughes, and Vought as principal subcontractors. It was produced from 1988 to 2000.[6][1][7] The bomber can drop conventional and thermonuclear weapons,[8] such as up to eighty 500-pound class (230 kg) Mk 82 JDAM GPS-guided bombs, or sixteen 2,400-pound (1,100 kg) B83 nuclear bombs. The B-2 is the only acknowledged in-service aircraft that can carry large air-to-surface standoff weapons in a stealth configuration. Development began under the Advanced Technology Bomber (ATB) project during the Carter administration, which cancelled the Mach 2-capable B-1A bomber in part because the ATB showed such promise, but development difficulties delayed progress and drove up costs. Ultimately, the program produced 21 B-2s at an average cost of $2.13 billion each (~$4.17 billion in 2024), including development, engineering, testing, production, and procurement.[9] Building each aircraft cost an average of US$737 million,[9] while total procurement costs (including production, spare parts, equipment, retrofitting, and software support) averaged $929 million (~$1.11 billion in 2023) per plane.[9] The project's considerable capital and operating costs made it controversial in the U.S. Congress even before the winding down of the Cold War dramatically reduced the desire for a stealth aircraft designed to strike deep in Soviet territory. Consequently, in the late 1980s and 1990s lawmakers shrank the planned purchase of 132 bombers to 21. The B-2 can perform attack missions at altitudes of up to 50,000 feet (15,000 m); it has an unrefueled range of more than 6,000 nautical miles (11,000 km; 6,900 mi) and can fly more than 10,000 nautical miles (19,000 km; 12,000 mi) with one midair refueling. It entered service in 1997 as the second aircraft designed with advanced stealth technology, after the Lockheed F-117 Nighthawk attack aircraft. Primarily designed as a nuclear bomber, the B-2 was first used in combat to drop conventional, non-nuclear ordnance in the Kosovo War in 1999. It was later used in Iraq, Afghanistan, Libya, Yemen, and Iran.[10][11] The United States Air Force has nineteen B-2s in service as of 2024.[12] One was destroyed in a 2008 crash,[13][14] and another was likely retired from service after being damaged in a crash in 2022.[12] The Air Force plans to operate the B-2s until 2032, when the Northrop Grumman B-21 Raider is to replace them.[15]