The account
The tunnel began behind a cover installation in West Berlin and reached toward communications cables under the Soviet-controlled side. Operation Gold turned digging into espionage: steel-lined passageways, concealed earth and taps on lines carrying an adversary's conversations. Collection began in May 1955. But another secret ran beside the tunnel. George Blake, a Soviet mole inside British intelligence, had already told the KGB about the project while it was being planned.
Following the trail
Documented interception operation compromised during planning
The CIA's public history documents the tunnel and Blake's disclosure. It explains that the KGB allowed the operation to continue to protect him, before arranging its discovery in April 1956. The agency's retrospective assessment holds that much of the collected material was genuine and valuable. That assessment matters: Soviet foreknowledge does not automatically mean every conversation carried on the tapped lines was planted disinformation.
Why it stays with us
The familiar question—did the other side know?—has an unsettling answer here: yes, but knowing did not make immediate exposure the best choice. The tunnel collected one secret while its continued existence protected another. The case makes espionage feel less like a locked cabinet being opened than a room in which several people are quietly pretending not to notice each other.
Follow the sources 1
- Berlin Tunnel: America's Ear Behind the Iron Curtain ↗Central Intelligence Agency