No single operation more typifies Berlin's importance as a strategic intelligence base then the construction of the Berlin Tunnel. Probably one of the most ambitious operations undertaken by the CIA in the 1950s, it succeeded despite the fact that the KGB knew about the operation even before construction of the tunnel had began!

The genesis of the tunnel operation lay in Berlin's location in Europe and its prewar status as the capital of a militarily and economically dominant Germany. The largest city on the Continent, Berlin lay at the center of a vast network of transportation and communications lines that extended from Western France to deep into Soviet Russia and Eastern Europe. This was still true in the 1950s; Soviet telephone and telegraph communications between Moscow, Warsaw, and Bucharest were routed through Berlin, for example. This became a factor of crucial importance beginning in 1951, when the Soviets began to shift from wireless communications to encrypted land lines for almost all military traffic. Land lines existed in two forms: overhead lines strung from telephone poles and underground cables. Both carried encrypted messages as well as nonsecure voice communications.

CIA officers examining this situation in 1952 concluded that underground cables offered the more valuable target, since they were buried and hence not subject to constant visual surveillance. If a tap could be placed covertly, it would be likely to remain in place for some time. Thus was born the idea of tunneling into the Soviet sector of Berlin to tap into Soviet military communications. The concept was tested in the spring of 1953, when an agent in the East Berlin telephone exchange patched an East Berlin telephone line into West Berlin late one night to sample what might be obtained. Even after midnight the communications traffic was sufficiently valuable that CIA Headquarters decided to go ahead with the operation.

During 1953, CIA continued to gather data and test the idea of tapping communications in East Berlin. By August 1953, detailed plans for the tunnel were completed and a proposal was drawn up for approval by DCI Allen Dulles. After much discussion, this was obtained on 20 January 1954.

Having learned the location of the underground cables used by the Soviets from an agent inside the East Berlin post office, the Altglienicke district was selected as the best site for a cable tap. Work began in February 1954, using the construction of an Air Force radar site and warehouse as a cover. The tunnel itself was completed a year later, at the end of February 1955, and the taps were in place and operating shortly thereafter.

Unfortunately, the whole operation was blown even before the DCI approved the project. On 22 October 1953, US intelligence officers briefed a British Secret Intelligence Service (SIS) audience that included KGB mole George Blake. Blake reported the existence of the tunnel project during his next meeting with his case officer, Sergei Kondrashev, in London the following December. However, a full report was not sent to Moscow until 12 February 1954.

Although the KGB was aware of the potential importance of the tap, its first priority was to protect Blake. Knowledge of the tunnel's existence was very closely held within the KGB--neither the GRU (Soviet military intelligence) nor the East German Stasi was informed. Rather than immediately shutting down the tunnel, the Soviets thus implemented a general tightening up of security procedures. A small team was formed to secretly locate the tap, which they did by late 1955. Early in 1956 the Soviets developed a plan whereby the tap would be "accidentally" discovered without putting Blake at risk. On the night of 21-22 April 1956, a special signal corps team began to dig. By 0200 they had discovered the tap chamber. At 1230 the following day they opened a trapdoor leading from the tap chamber down a vertical shaft to the tunnel. By 1420 they had penetrated the tunnel in the full glare of a well-organized publicity coup.

The digging operation had been seen from an observation post atop the warehouse in West Berlin and the tunnel evacuated long before the Soviets entered the tap chamber. A microphone was left in place to record what was going on. The Soviet publicity coup backfired: rather than condemning the operation, the non-Soviet press hailed it as audacious and well-planned. Of course, at the time, no one knew the extent of Soviet foreknowledge.

Since KGB archives remain closed, we cannot be certain that the Soviets did not exploit their prior knowledge of the cable tap for their own purposes--to plant false information, for example. However, according to former DCI Richard Helms, the possibility that the Soviets used the tunnel for "disinformazia" (disinformation) was closely examined after Blake's exposure and arrest in 1961. Finally, it was concluded that the intelligence that had been collected was genuine.

The sheer volume of the "take" from the tunnel operation would tend to support that conclusion. In all, about 40,000 hours of telephone conversations were recorded, along with 6,000,000 hours of teletype traffic. Most of the useful information dealt with Soviet orders of battle and force dispositions--information that was invaluable in the days before reconnaissance satellites and other, more sophisticated means of collection became operational. Not until more than two years after the tunnel was exposed and shut down was the task of processing this immense volume of data completed.

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