I thought Diego Garcia was ours. My father used to go there in the late 70s.
I went to Diego Garcia for about six months in 1981.
I was working on a tanker that was chartered to the Navy.
The island was British; anyone engaged in criminal activity was sent to Hong Kong for trial.
In the morning, the British national anthem was played before ours.
IIRC Diego Garcia was leased as part of the WW2 lend-lease deal.
I believe the lease on DG is up and is being renegotiated even as we speak.