The British-built Kestrel was designed with vertical/short takeoff and landing capabilities, making it possible to operate from grass or semi-prepared surfaces offering great operational flexibility. Four adjustable exhaust nozzles beneath the wing roots could be rotated to provide thrust for vertical, backward or hovering flight as well as conventional forward movement.

The first Kestrel began conventional flight trials on March 13, 1961, in Britain. In 1962 the governments of the United States, Britain and the Federal Republic of Germany ordered nine aircraft for combined testing by those countries' representatives. They formed an evaluation squadron that conducted Kestrel trials between April and September 1965. Six of these trial aircraft were later delivered to the United States where, as XV-6As, they underwent additional testing of V/STOL fighter techniques. An improved version, known as the Harrier (AV-8), became the world's first operational V/STOL fighter when it entered Royal Air Force service in 1969.  In 1970 the U.S. Marine Corps ordered 102 AV-8A Harriers and two trainers (TAV-8A). 

A licensing agreement was concluded with McDonnell-Douglas for the manufacture of the follow-on AV-8B Harrier II in the United States.  The initial production order of twelve AV-8Bs was delivered to the U.S. Marines in January 1984.

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