The McDonnell Douglas F-4 Phantom II[1][2] is a tandem two-seat, twin-engined, all-weather, long-range supersonic jet interceptor fighter/fighter-bomber originally developed for the United States Navy by McDonnell Aircraft.[2] It first entered service in 1960 with the U.S. Navy. Proving highly adaptable, it was adopted by the U.S. Marine Corps, and U.S. Air Force by the mid-1960s and became a major part of their air wings.[3] The Phantom is a large fighter with a top speed of over Mach 2. It can carry over 18,000 pounds (8,400 kg) of weapons on nine external hardpoints, including air-to-air and air-to-ground missiles, and various bombs. The F-4, like other interceptors of its time, was designed without an internal cannon, but later models incorporated a cannon. Beginning in 1959, it set 15 world records,[4] including an absolute speed record, and an absolute altitude record.[5] The F-4 was used extensively by these three U.S. services during the Vietnam War, serving as the principal air superiority fighter for both the Navy and Air Force, as well as being important in the ground-attack and reconnaissance roles by the close of U.S. involvement in the war.[3] The Phantom has the distinction of being the last U.S. fighter flown to attain ace status in the 20th century. During the Vietnam War, the USAF had one pilot and two WSOs,[6] and the US Navy one pilot and one RIO, become aces in air-to-air combat.[7] It continued to form a major part of U.S. military air power throughout the 1970s and 1980s, being gradually replaced by more modern aircraft such as the F-15 Eagle and F-16 Fighting Falcon in the U.S. Air Force; the F-14 Tomcat and F/A-18 Hornet in the U.S. Navy; and the F/A-18 in the U.S. Marine Corps.