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A Look Back ... The Berlin Tunnel: Exposed

In the rainy, early hours of April 22, 1956, a team of Soviet and East German soldiers began to dig at the municipal cemetery in Altglienicke in East Berlin. It had been an extremely rainy spring and there had been many short circuits in Berlin’s telephone network. The soldiers’ assignment was to unearth a buried telephone cable and check for damage. When they reached the cable, they made an amazing discovery: the cable was tapped and rerouted into a tunnel. The Berlin Tunnel (a.k.a. Operation Gold) was exposed.


The Need for Intelligence

Berlin Map

During the Cold War, monitoring and thwarting the Soviet Union’s influence worldwide was the top priority of the CIA. Berlin stood on the front lines of the superpower conflict. The East German capital was the center of a communications network connecting key European nodes and extending well into Russia. Soviet telephone and telegraph communications between Moscow, Warsaw, and Bucharest were routed through the city.

By the early 1950s the Soviets had shifted from radio to land line telephones for most military traffic, transmitting both encrypted messages and nonsecure voice communications. CIA assessed that tapping the underground cables could be done securely and with little notice. Following a similar success in Vienna in 1951, the CIA and the British Secret Intelligence Service developed a tunneling and tapping plan that Director of Central Intelligence Allen Dulles approved in January 1954; work began the following month. The construction used an Air Force radar site and warehouse as a cover and proceeded undetected.

Building the tunnel was an undertaking of extreme proportions. During construction:

  • 3,100 tons of soil were removed, which would fill more than 20 living rooms in an average American home
  • 125 tons of steel liner plate were used to line the tunnel
  • 1,000 cubic yards of grout were consumed

The finished tunnel was 1,476 feet long.

British technicians installed the taps. Collection began in May 1955.


A Mole in Our Midst

tunnel interior
Tunnel interior with wooden rails for forklift and sandbag 'benches' for utility lines and ventilation.

Unfortunately, the KGB—the Soviet Union’s premier intelligence agency—had been aware of the project from the start. George Blake, a KGB penetration of the British Secret Intelligence Service (also known as MI-6), knew about the operation and apprised the Soviets about it during the planning stages. It has been determined that there were no known attempts to feed disinformation to the CIA. The Soviet military continued to use the cables for communications of intelligence value.

Most likely, the KGB did not reveal that it knew about the Tunnel to protect Blake. In April 1956 the KGB sent a team to “discover” the Tunnel while repairing faulty underground cables. CIA officers monitoring the area saw the digging and vacated the tunnel before the Soviets closed it down. Moscow had hoped to win a propaganda victory by publicizing the operation, but most press coverage instead marveled at the United States’ technical ingenuity.


An Intelligence Success

The Berlin Tunnel episode illustrates how elements of success and failure can be found in the same intelligence operation. The cable taps yielded enormous amounts of intelligence on a hard target and answered important strategic questions for US policymakers and warfighters. The success in numbers includes:

  • 50,000 reels of tape
  • 443,000 fully transcribed conversations (368,000 Soviet and 75,000 East German)
  • 40,000 hours of telephone conversations
  • 6,000,000 hours of teletype traffic
  • 1,750 intelligence reports

At the same time, a Soviet penetration of British intelligence compromised the costly operation to the KGB after less than a year and raised persistent (but ultimately disproven) concerns that the Soviets had used it to purvey disinformation. The Berlin Tunnel was probably one of the most ambitious operations undertaken by the Agency in the 1950s, and it succeeded despite the fact that the KGB knew about it before construction even began.

CIA’s official history of the Berlin Tunnel has been declassified and is available in the Freedom of Information Act Electronic Reading Room.


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Historical Document
Posted: Jun 26, 2009 02:14 PM
Last Updated: Apr 30, 2013 12:14 PM