The B-2 is the only stealth strategic bomber in the world today. The main feature is low detectability, which is commonly known as stealth. It can make it safe to attack through a tight air defense system. The stealth of the B-2 is not limited to the radar detection level, but also includes the reduction of different signals such as infrared, visible light and noise, so that the possibility of detection and locking is minimized. In the absence of refueling in the air, the B-2 can reach 12,000 kilometers in combat and 18,000 kilometers in air refueling. The air flight time per mission is generally not less than 10 hours, and the United States Air Force claims that it has "global arrival" and "global destruction" capabilities. The stealth performance of the B-2 can be compared with that of a small F-117 attack aircraft, while the combat capability is similar to that of a huge B-1B bomber. In 1997, the first six B-2 bombers officially entered service and produced only 21 aircraft. The cost of each B-2 is 2.4 billion U.S. dollars. If the weight of the B-2 is measured, the unit weight of the B-2 is higher than that of the gold at the service time.