The Lockheed Martin F-22 Raptor is an Advanced Tactical Fighter aircraft developed by Lockheed Martin, Boeing, and Pratt & Whitney (engines). The air superiority fighter was primarily designed for the United States Air Force (USAF). Entering initial production in 2001, the aircraft is primarily operated by the Air Education and Training Command, Air Combat Command, and Pacific Air Forces within the Air Force. Despite plans to initially acquire up to 750 of the stealth jets, project costs and reliability concerns have limited the number of Raptors produced.