The status of the Occupying Powers was made clear to me during a couple of visits. First, the RAF Staff College visit in 1978 when we Brits plus the Americans on the course (all in uniform) went through Checkpoint Charlie with minimal fuss whilst all the other nationals in another coach had quite a difficult crossing. (Our Yugoslav MIG 21 pilot colleague, a fairly hardline communist, was outraged at such treatment of a comrade!) Some years later, my NATO Defense College course had Berlin as part of the European tour. The Belgian Air Force B727 that we used for transport was not permitted in the corridors and, as I recall, we flew in/out using Pan Am. And as this was a NATO rather than national visit, there was no question of anyone on the course going into the East on that occasion. (The wife of one of our US Army officers had grown up in East Berlin and, on the day they started to build the wall, she had crossed into the West. Prior to the tour, she had gone through all required formalities to see her family during the visit and, despite that, got a pretty hard time when going through Charlie.)