I was in the OM bar at Valley once in late 1975, chatting with an ATCO who had a nav brevet. He mentioned that he'd been on 60 Sqn at Wildenrath "Flying Air Marshals to NATO pi$$-ups and golf competitions".
"But didn't you also fly those Pembroke C(
PR) Mk1s I saw when I was holding there in the summer? Must have been useful when pottering up the Berlin corridors!"
He went very pale, grabbed me by the shoulder and took me over to a quiet corner. "I don't know how the hell you knew about that, but never mention it again to anyone - it's VERY classified!"
"I didn't know anything, just guessed. But you've now confirmed my guess. I will keep schtum though". And I did!!