The McDonnell Douglas/Boeing AV-8B Harrier II evolved from the British Hawker Siddeley P.1127 of 1957. In 1965, the United Kingdom, United States, and Germany funded evaluation of nine development aircraft known as Kestrels to investigate tactical jet vertical and short take-off and landing operations. The AV-8A Harrier became the first operational tactical jet of this kind when it joined the Marine Corps in 1971, replacing A-4s for close air support missions and allowing support of ground troops from nearby unimproved fields. The AV-8B Harrier II entered Marine service in 1985 with extensive changes from the AV-8A, including a new supercritical composite wing, increased fuel capacity, a new cockpit similar to the F/A-18, new propulsion nozzles, a bubble canopy, automatic stability control, and outrigger landing gear struts moved inboard from the wingtips. The Marines are replacing their Harriers with the F-35B. Bureau Number 161576, the fourth production AV-8B, flew at NAS Patuxent River with the Strike Aircraft Test Directorate, Naval Strike Aircraft Test Squadron, and Air Test and Evaluation Squadron Five before retiring in August 1999 and joining PRNAM's flight line in January 2019.