The pilots that flew the Spits were not happy changing over to something that was untested in combat. Although once the change over did happen they were very pleased with the P-51.
As for the British planes that were made in the US, we did send them to Great Britain, but they were the export versions that were bastages of the real thing.
For example we sent over the P-38 Lightning (an adopted British name) it was without the super turbo chargers, differnt engines, and non-counter-rotating props. It about made the plane all but useless.
Again we sent over the P-51 Mustang (also an adopted British name) again with no turbo chargers. It was the British who experimented with the Merline engine that made the P-51 the plane it was.
The Spitfires were well liked by the American pilots because they were fast and very maneuverable. They did not like the idea of giving up this ability with the new Mustang. How ever once they got the feel for them in combat they eventually liked them over the Spit.
