US, USAAF & USAF WW2 Airfields in the UK
As Stopstart says, all airfields were RAF (Whatever). They all had a very small contingent of RAF personnel to liaise with the Americans and to avoid giving the USAAF (and later, the USAF) US sovereign territory within those airfields, and therefore, negating UK laws.
The War Powers Act 1940 (as amended) is, I believe, chapter and verse.
A bit deep for a Sunday argument, isn't it?
I think I'm a bit sad for having an answer. I must get out more.