This is a very belated response to mike1964's post early on in this thread, in which he says: "I understand that Pembrokes (and perhaps other liaison types) flying into/out of Berlin during the Cold War were used for surreptitious reconnaissance" .
He is quite right. I was in the MOD in the late 1970s and early 1980s and saw many of the photos that were taken while flying along the corridor to and from Berlin. The photos would typically be annotated with a description of what was photographed eg. T-64 tank, ZSU-23-4 or MiG-21, although they were often of more mundane objects. I remember a series of fairly good quality "snaps" taken of a nudist camp, showing mixed groups playing volleyball. The photos were annotated simply as SSNB which we later learned meant Soft Skinned Naked Bodies.