It is a flying wing design with a crew of two. The bomber can deploy both conventional and thermonuclear weapons, such as up to eighty 500-pound class (230 kg) Mk 82 JDAM Global Positioning System-guided bombs, or sixteen 2,400-pound (1,100 kg) B83 nuclear bombs. The B-2 is the only acknowledged aircraft that can carry large air-to-surface standoff weapons in a stealth configuration. Twenty B-2s are in service with the United States Air Force, which plans to operate them until 2032 as of 2018, when the Northrop Grumman B-21 Raider is to replace it. The B-2 is capable of all-altitude attack missions up to 50,000 feet (15,000 m), with a range of more than 6,000 nautical miles (6,900 mi; 11,000 km) on internal fuel and over 10,000 nautical miles (12,000 mi; 19,000 km) with one midair refueling. It entered service in 1997 as the second aircraft designed to have advanced stealth technology after the Lockheed F-117 Nighthawk attack aircraft. Though designed originally as primarily a nuclear bomber, the B-2 was first used in combat dropping conventional, non-nuclear ordnance in the Kosovo War in 1999. It later served in Iraq, Afghanistan, and Libya. For details of development, design and operational history of the B-2 Spirit, click here.