In the late 1960s the United States Marine Corps fell in love with the idea of an attack airplane that could take-off and land vertically. In theory, that airplane could be based very close to the action on the battlefield because it wouldn't need a long runway to operate, and that short range would allow for quick close air support response times.
A couple of senior-ranking Marine pilots went to England to take a test flight in the British Harrier, and they were impressed enough to convince the Pentagon budgeteers to buy the service 110 of them. Since DoD had a thing about foreign-built hardware, they came up with a special arrangement where the airplanes were manufactured in England and assembled in America.
Starting in 1971, Marine Corps AV-8A Harrier squadrons were stood up at Yuma and Cherry Point. Because of the unique flight characteristics, only the best pilots were accepted for Harrier training. Unfortunately, in too many cases no amount of stick-and-rudder talent was enough to make up for an airplane that was poorly designed and overly ambitious, performance-wise, for the technology of the day.
Marine Air lost 55 AV-8As between 1971 and 1982. The Harrier had a Class A mishap (over $1 million in damage or aircraft destroyed) rate of 39 per 100,000 flight hours -- the worst in modern military aviation history by far. Some of the mishaps were due to the inherently dangerous aspects of the attack mission -- like dropping bombs in a steep dive and flying close to the ground in mountainous terrain -- but about half of them happened in the vertical flight regime, the thing that made the Harrier unique.
The Harrier's vectored thrust is what gives it the ability to take-off and land vertically and hover like a helicopter. Unlike the Harrier II that has a computer interface that prevents the pilot from accidently commanding the nozzles in a way that would throw the airplane out of balance, the first version of the jump jet required that the pilot manually adjust each throttle precisely to maintain a hover or to launch or land vertically. The result was an airplane that pilots described as "unforgiving" and that other tactical jet communities labeled as a "widow maker."
Now watch this awesome documentary about the Harrier: