During the Cold War, monitoring the Soviet
Union and its influence worldwide was the top priority for the CIA. In the 1950s, before
reconnaissance satellites and other sophisticated collection systems were operational, wiretaps
were one of the most important technical means for collecting intelligence about Soviet military
capabilities. The challenge was where and how to best conduct such wiretap operations.
Berlin was at the center of a vast communications network from France to deep within Russia
and Eastern Europe. At the time, almost all Soviet military telephone and telegraph traffic
between Moscow, Warsaw, and Bucharest was routed through Berlin over land lines strung
overhead and buried underground. In a joint effort, the CIA and the British Secret Intelligence
Service, MI-6, assessed that tapping into underground communication lines in the Soviet
sector of Berlin offered a good source for Soviet and East German intelligence.
Tunneling from West Berlin to the underground cables in nearby East Berlin was judged to
be feasible, and Director of Central Intelligence Allen Dulles approved the covert tunneling
and tapping operation in January 1954. Work began the following month using a US Air Force
radar site and warehouse in West Berlin as cover.
Construction took a year. Tunnelers removed 3,100 tons of soil and used 125 tons of steel
plate and 1,000 cubic yards of grout. The finished tunnel was 1,476 feet long. British
technicians installed the taps, and collection began in May 1955.
Unknown to CIA and MI-6, the KGB—the Soviet Union’s premier intelligence agency—had
been aware of the project from its inception. A KGB mole inside MI-6 had alerted the Soviets
during the operations planning stages. To protect their source, the KGB allowed the
operation to continue until April 1956, when they “discovered” the tunnel while supposedly
repairing faulty underground cables. The Soviets hoped to stage a propaganda coup by publicizing
the operation, but their plan backfired when, instead of condemning the operation, most
press coverage marveled at the operation’s audacity and technical ingenuity.
The taps collected successfully for nearly a year, and processing the immense volume
of data took more than two years after the tunnel was shut down. Subsequent studies determined
that the Soviets had not attempted to feed false information over the lines—the intelligence
that had been collected was genuine. Despite the KGB’s foreknowledge, CIA ruled this
most ambitious operation a success, yielding valuable intelligence for US policymakers