The Phantom is a large fighter with a top speed of over Mach 2.2. It can carry more than 18,000 pounds (8,400 kg) of weapons on nine external hardpoints, including air-to-air missiles, air-to-ground missiles, and various bombs. The F-4, like other interceptors of its time, was initially designed without an internal cannon. Later models incorporated an M61 Vulcan rotary cannon. Beginning in 1959, it set 15 world records for in-flight performance,[4] including an absolute speed record, and an absolute altitude record.[5]The F-4 was used extensively during the Vietnam War. It served as the principal air superiority fighter for the U.S. Air Force, Navy, and Marine Corps and became important in the ground-attack and aerial reconnaissance roles late in the war. During the Vietnam War, one U.S. Air Force pilot, two weapon systems officers (WSOs),[6] one U.S. Navy pilot and one radar intercept officer (RIO) became aces by achieving five aerial kills against enemy fighter aircraft.[7] The F-4 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 in the U.S. Navy, and the F/A-18 Hornet in the U.S. Navy and U.S. Marine Corps.