The USMC Harriers were, however, built under license by a US aviation company. Ditto a bunch of other British-designed aircraft used by the USAF, such as the English Electric Canberra aka Martin B-57 Canberra:

https://en.wikipedia.org/wiki/English_Electric_Canberra

https://en.wikipedia.org/wiki/Martin_B-57_Canberra

(This traffic went in both directions: for example the British Army's AH-64D Apache Longbow gunships are built by Westland.)