Tuesday, June 09, 2009

The Berlin Tunnel

One of the most spectacular SIGINT operations in the Cold War era was project PBJOINTLY, the Berlin tunnel. It was a CIA operation to tap the three main Soviet communications cables in the Soviet-occupied sector of Berlin. Planning and construction lasted for five years and started in the late 1940's with penetrating the office of the East German post to covertly obtains plans of the Soviet network. In 1952, they had all information to determine the ideal location for the tap, and trial tappings on other locations were performed.

It became a joint operation between the US and British intelligence. Mid 1953, construction planning started. The US Engineering Corps would dig the 1500 feet (500 m) tunnel underneath the East German border and the British would drive the vertical shaft towards the cables, only 27 inches (68 cm) beneath the surface alongside a highway, and provide the tapping of the cable. Some 3,000 tons of sand had to be disposed without border guards noticing it. A warehouse project near the tunnel was set up as cover and the tunnel dirt was disposed in its basement. All planning and work had to be done in absolute secrecy, with as little as possible people involved. Meanwhile, linguists in Russian were recruited and trained.

In August 1953, tunneling started, right beneath border guards, forcing engineers to halt and keep silent, each time the guards walked over. By March 1955 the tunnel and the tap room, a large air-conditioned sealed room with electronics, were completed. The three main Soviet landlines were tapped, the signals preamplified in the tap room and sent further down the tunnel for recording. It was a marvel of planning and engineering. The cables carried 1200 channels. 28 telex circuits and 121 voice channels were recorded continuously, transcribed and analysed.

Nonetheless, on April 21, 1956, after eleven months of eavesdropping, the tunnel was discovered. Apparently by accident, when East Germans dug up a faulty cable. However, later on, British intelligence discovered that George Blake, an MI6 officer who was involved from the earliest beginning of the planning, had been recruited by the KGB as early as 1952. He informed his Soviet contacts as soon as the final location of the tunnel was planned. The tunnel and the mole, what's in a name.

At the end, the question remains how successful the 6.7 million dollar operation was, and to whom. The Soviets knew right from the start, but could not react as this would compromise their MI6 mole. Why did they allow eleven months of tapping? What was the value of the intercepted intelligence? Did the Russians fed the CIA with fake and misleading information? Was this a magnificent intelligence coup by the West, or one by the East? We'll never know...

More information about the tunnel and its construction in this CIA document (pdf 3.4 Mb), published on the FAS. It includes all technical aspects, describes the aftermath of the operation and the complete report on the discovery by the Soviets. On the CIA Studies in Intelligence pages you will find many original CIA documents regarding the Berlin Tunnel and on this page an account of one of the operations officers. Below a Cold War Spies video which includes an interview with George Blake.

Update: Operation Ivy Bells was the undersea equivalent of the Berlin tunnel. Read more about the tapping of the Soviet cable in the Sea of Okhotsk in my September 2010 post.

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