Berlin Tunnel: America's Ear behind the Iron Curtain

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 and warfighters.