I flew in a USAF TFW over 1969-70 in SVN, but that was before I joined the RAF, so I don't qualify for the thread title.
But I did a weekend visit in 1970 down to stay with FACs in Ca Mao, in the southern delta (then IV Corps in SVN). While I was having a beer with the FACs, this Brit came over for a beer (or two). He had been ex-Brit Army, or perhaps RM, and was serving in a mercenary role leading out small long-range patrols on search and destroy. Perhaps I should say he wasn't "leading" - he would bring up the tail as he didn't want to be shot in the back.
He had previously served in this role in Africa, Congo I think. He had several chain type scars across his face, so had been in the wars. We drank for the afternoon, then we piled into his jeep and went off-base to a civvie-type house. This was the local Ca Mau CIA chief's house. We had a very pleasant BBQ, sitting around a large table with all the CIA chaps - and their wives!! And me, still in my sweaty flying suit. Eventually my new-found Brit mate and I stumbled off and back to base in his jeep. Ahhhh, happy days.