picked the Harrier in 1968, as no other aircraft could do the job it promised, they did not care much about max speed (hardly needed in CAS) or a heavy weapon load or loiter, they saw a platform capable of very rapid deployment from helicopter carriers, that could later be deployed from very makeshift facilities ashore, and quickly.
Being relatively simple to maintain helped too, though the AV
-8A was simpler avionically than the RAF Harriers, with their dedicated central Europe low level role.
They had to fight long and hard against an ingrained Not Invented Here syndrome in Congress and the Pentagon, but they were happy to make savings to buy the Harriers by canceling some Phantom F-4Js.
The point is, this coincided with the USAF
competition to produce a new close support aircraft, eventually with a competion between the Northrop A-9 and Fairchild A-10, the USMC
clearly were not interested, as they had a different requirement in mind, that only the Harrier could satisfy.
So, they ended up buying just over 100 AV
-8As from Hawkers at Kingston in the UK.
Later of course they led the development of the AV
-8B with MDD, with improvements in payload/range, again with much opposition, Congress would have preferred that USMC
would just stick to F-18s.
F-18s that needed either a concrete runway or large aircraft carrier, the detractors were missing the point again, or just not listening.
should be commended for holding out for what they required against much opposition.
In the 1991 Gulf War, USMC AV
-8Bs clocked up an enviable sortie rate, they were the fastest reacting strike assets in theatre then as well as last year in Iraq, but the continuing anti Harrier lobby don't want to hear that.
The RAF found the Harrier not to have a significantly higher attrition rate compared to other types regular use in the low level strike/attack role, (in until the early 90's the RAF did more low level than USMC
However at the start, the RAF only put very experienced types through the Harrier conversion course, they also included some helicopter training as part of the course.
Advice the USMC
apparently did not heed in the early days.
The Harrier is underpowered in the same way the F-18 is short on range, both are still highly effective in their respective roles.
A-10 was a Vietnam era requirement for close support, that with the addition of the GAU-8 cannon, became a very effective close support aircraft, especially in the Cold War anti tank role.
It's another unique type somewhat unloved by the top brass, but A-10 is not capable of being deployed from small flat tops and still needs a concrete runway, even an austere one.