Dad was an Army officer from WWII to 1966. His last tour was at the Pentagon, I believe on the staff of the Under Secretary of the Army. Anyway I recall him flying to London with his boss to brief the Brits on some weapons program. Secret stuff. Dad’s in his 90s now and still with a good mind. Not long ago he mentioned that trip, so I asked him “what was it that you briefed the Brits about?” He looked at me with a jaundiced eye and said “You’re not cleared.” And that was that.
My nephew works at State. He’s overseas now, but when he’s working in DC he won’t even tell me which building he goes to. “Sorry. Classified.”