It would have been around 1988 when Mrs Thatcher, as PM, came out to NATO HQ to address the Council - for, I think, her first time there. It was a bravura performance, at a time when Cruise Missile deployment in Europe was a hot topic, and our allied military counterparts were lavish in their praise for it.
It's also worth adding that she developed a special relationship with 10 Squadron over many VIP trips, to the extent that she agreed to present the unit's current standard in 1988, and eventually earning a special Logbook to mark those flights.