The McDonnell Douglas F-4 Phantom II[2] was a two-seat supersonic long-range all-weather fighter-bomber produced for the United States military by McDonnell Douglas. Entering service in 1960, the F-4 was designed as the first modern fleet defense fighter for the United States Navy. By 1963, it was adopted by the United States Air Force for the fighter-bomber role. When production ended in 1981, 5,195 Phantom IIs had been built, making it the most numerous American supersonic military aircraft. Until the advent of the F-15 Eagle, the F-4 also held a record for the longest continuous production with a run of 24 years. Innovations in the F-4 included an advanced pulse-doppler radar and extensive use of titanium in the airframe.