The only foreign aircraft in U.S service, that's why Carter tried to cancel it, because being arrogant, and thinking his country was superior, he thought they shouldn't have to use other countries planes, even his allies.
The AV-8C (Harrier II plus) is the same as the RAF Harrier Gr.5 but with improved NV equipment. This said, the RAF Gr.7 is the same as Gr.5 but with improved avionics, and the same NV equipment as the AV-8C. In short, the GR.7 has improved avionics over the AV-8C.