What with Filingdales in Yorkshire, Greenland & the"Dew Line" we had them tagged well before they got near & would send up a welcoming party.
The scene - NATO exercise over the North Sea, c1975. Self in tanker on CAP getting slightly bored.
Northern Radar "(c/s) look in your 2 o'clock, friendly traffic on a reciprocal heading, slightly low, will pass clear"
Captain, "Roger, looking, will report visual"
Nav Radar (self) looks out of little window by left shoulder (I'm facing backwards remember) and sees two Soviet Badger bombers pass by in exactly the position predicted by Northern Radar. Reports to captain.
Captain. "Contact the traffic. Define "friendly" please?"
Had them tagged? Well not always!