On the MiG-21: "It had no gas – a point-defense fighter.
About five years ago, I was waiting for a flight from Hanoi to Saigon, when ATC shut down civil flights and six VNAF Mig-21s launched. A spectacular sight.
The airport remained closed and 20 minutes later, all the Migs returned! Point defence indeed.
Incidentally, Hanoi Nội Bài is the civil side of what was the Phúc Yên airbase during the war. It was a frequent target of US strikes and the airfield is surrounded by bomb craters, which the resourceful locals filled with water and turned into fish ponds. Just to the north of the airfield is the infamous Thud Ridge.