Betrayal in Berlin – a small but important part of the Cold War story

The Berlin Tunnel was an Anglo-American eavesdropping operation mounted against Russian-controlled East Berlin in 1955–56.  It was a technical and engineering triumph which yielded a vast hoard of intelligence and, crucially, guaranteed early warning of any surprise Russian attack (as was mooted by the Russian military). Yet it was betrayed to the Russians by the British spy George Blake before a single sod was dug.