Spies Beneath Berlin

Operation Stopwatch/Gold, said CIA chief Alan Dulles, was one of the most valuable and daring projects ever undertaken. In 1955 it ran a tunnel 800 metres under the Russian sector of Cold War Berlin, and for more than a year tuned into Red Army intelligence. This was an almost impossible trick: apart from the technical wizardry needed, any noise or vibration could have given the game away. When snow fell panic measures were suddenly needed to prevent it thawing in a tell-tale line leading to the target building.