The F-4 Phantom II was a twin-engine, all-weather, fighter-bomber. The Phantom was first used by the U.S. Navy as an interceptor but also was capable of flying as a ground-support bomber for the U.S. Marine Corps. The aircraft could perform three tactical air roles,air superiority, interdiction and close air support,as it did in southeast Asia. McDonnell designed one of the greatest fighters of the postwar era as a company venture to meet anticipated future needs. Planned as an attack aircraft with four 20mm guns, it was quickly changed into a very advanced gunless all-weather interceptor with advanced radar and missile armament. The aircraft flew every traditional military mission: air superiority, close air support, interception, air defense suppression, long-range strike, fleet defense, attack and reconnaissance.