Its said that the RAF operated a Vickers Valetta which regularly flew along the corridors armed with cameras placed at an angle to photo into East Germany and 192 Squadron used a Varsity in the corridors to train its signals specialists.
It was in these corridors that the RAF suffered a cold war loss when MiG fighters shot down a Lincoln in 1953 which was on "routine training flight" (RAF) or had "penetrated 75 miles into East Germany" (Soviet source). It has been alleged that this flight was used to provoke Soviet defences to gauge their reaction but who knows. This incident has been mentioned in a previous Prune thread in 2003 from which I quote Archimedes
I found the reference to the Lincoln being armed - it was in Tony Geraghty's history of Brixmis. The Brixmis team that went out to the crash site was, apparently, convinced that the guns were loaded, and that the BOI report (which blamed the navigator for getting lost) was inaccurate. Subtext being that the affil ex was just a cover.
This, of course, doesn't mean that the Brixmis team got it right (for instance, the Russians might have been tempted to doctor the crash site by introducing 20mm ammo to the scene... - 'We are very sorry, comrade, but you will understand that once the aircraft fired at our fighter...') - but it is an interesting little tale...