Cold War, Military

Cold War Stories: The CIA & The Berlin Phone Tap Tunnel

In the early 1950s, the Central Intelligence Agency (CIA) was frustrated. As the Soviet Union solidified its hold on Eastern Europe, the Agency was utterly unable to eavesdrop on the Soviet military.

The situation seemed worse as the blackout on information was relatively new. For several years, beginning in World War II, American intelligence had been able to crack Soviet codes. This allowed them to monitor extremely secret communications from Moscow. But at some point the Soviets stopped using radio signals for its most secret messages. They switched to landlines, making interception impossible.

The Beginning

The CIA needed to somehow tap into the telephone lines the Soviets were using. Beginning in 1951 a wildly ambitious plan was developed in conjunction with Britain’s Secret Intelligence Service. Called Operation Gold, it would send a tunnel a quarter-mile under Soviet-controlled territory to install taps on buried communication cables. If the plan worked, recordings of voice and signal traffic could then be analysed in Washington and London.

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The project, which required two years of extensive planning, eventually succeeded in tapping into telephone cables under East Berlin. However, the tunnel was discovered by the Soviets after being operational for about a year. The story at the time was that a Red Army communications team, sensing through electronic means that a tap was in place. This narrowed down the location and happened upon the tunnel.

In time it came out that George Blake, a British intelligence agent who was secretly working for the Soviets, had tipped Moscow off about the tunnel while it was still being planned. Operation Gold had always been compromised.

Yet the KGB’s strategic decision not to act upon Blake’s information ensured that the CIA’s tunnel was still an astounding success.

The Planning

The requirements for the tunnel were, of course, unusual. It would begin in West German territory and cross into East German territory. Its entrance had to be hidden, and it had to be dug silently. Complicating things even more, the “spoil,” the earth removed from the ground, couldn’t be seen being transported from the site.

U.S. Army Tanks in Berlin facing off against East German Police (U.S. Army photo)

The solution was to construct a warehouse as the starting point of the tunnel. A deep basement would hold the dirt removed from the tunnel. And the main floor of the warehouse would hold electronic equipment to monitor the communication cables.

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At a meeting with British intelligence officials, a CIA engineer suggested using steel liner plates to build a tunnel six feet in diameter. That plan was accepted, as was a plan to dig the tunnel using a shield. This was a metal face that would be slowly moved forward as earth was removed. The US Army Corps of Engineers would provide the team that would do the digging. They’d also assemble the tunnel’s steel walls as it moved forward.

Doing the Maths

A CIA engineer was tasked with mathematical calculations concerning the weight that would be pressing on the tunnel. One tricky problem: the tunnel would pass under a highway that would be used by trucks or even Soviet tanks. In the early planning, no one knew the precise target location for the tunnel.

The CIA had been trying to learn which telephone cables might carry Soviet military traffic. A defector provided highly useful information. His knowledge of telephone cables in East Germany indicated that some cables were quite close to the modern borders. A tunnel, started from the right place, could conceivably reach them.

Some of the cables dated back to the 19th century, but they carried current traffic which included Soviet military communications. And intelligence indicated that highly coveted traffic between Moscow and Red Army bases in Eastern Europe flowed through those cables.

The Digging

The Berlin tunnel project became a CIA priority. It included approval from the Agency’s director, Allen Dulles, and President Dwight Eisenhower. The Agency appointed a former FBI agent, Bill Harvey, to lead the Berlin station. 

Harvey was an unusual choice to lead the Agency’s efforts in a city that was such a focus of Cold War intrigue. A former FBI agent known for prodigious drinking, he had no overseas experience at all. But the top people at the CIA sensed that Harvey was the sort of hard-charging fellow who could get things done.

Security on the Berlin tunnel project was exceedingly tight. At some point the CIA realized it should involve British intelligence. The British already had valuable experience tapping telephone cables. Harvey was wary. He had been one of the first CIA people to suspect that Britain’s Kim Philby was a Soviet mole. And his hunch had been proven correct. But the CIA needed the British help, so Harvey put his suspicions aside. And George Blake, a Soviet spy working in the British SIS, was thus made aware of Operation Gold.

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A site was selected in a rural part of Berlin. A field was rented from a farmer, and the U.S. Army began building the warehouse from which the tunnel would begin.

The Construction

In the U.S., a team of workers was recruited from the Army Corps of Engineers. A CIA official visited various Army bases and found specialised workers. These included electricians and sheet metal workers, who already had a security clearance. Within a few weeks a highly skilled and trustworthy team was assembled.

On the 24 April 1956, the tunnel was opened to the press. Both sides claiming a victory.

The men who would actually dig the tunnel were briefed on the construction technique, but were not yet told where the tunnel would be dug. In the summer of 1954, they were sent to a base in a remote part of the American Southwest to practice. They were using the specially constructed tunnel shield. After getting familiar with the parts of the tunnel they’d be assembling underground, they practiced by successfully digging a 50-foot tunnel. The components for the tunnel were then shipped to Berlin.

The cover story was that the warehouse would be housing some sort of radar installation. Both sides operated radar units to track flights in the area. However, East German soldiers on the other side of the border did occasionally watch the new American warehouse with binoculars. The Americans kept them entertained by periodically moving a radar antenna on the roof. The antenna wasn’t connected to anything inside the warehouse.

A Washing Machine!

The soldiers posted to the warehouse lived in a small barracks on the site. To fit the cover story about the radar installation, the men from the Corps of Engineers were issued uniforms with insignia showing them to be in the Signal Corps.

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The tunnel began on September 2, 1954. The men had to dig by hand, to work silently. They used infantrymen’s entrenching tools, small folding shovels that were easy to handle in the cramped conditions. The work proceeded well, despite a few unanticipated problems. The water table was higher than the engineers had estimated. The tunnel was then dug about ten feet below the surface, about half the distance originally planned.

The work was soon proceeding steadily. The diggers operated in three shifts around the clock, and were moving forward at about 11 feet a day. When the CIA’s Bill Harvey made one of his visits to the tunnel, the former G-Man noticed a problem. The diggers were getting their uniforms very dirty. It would look suspicious if anyone, East German, Soviet, or even other Americans, noticed Signal Corps personnel in heavily soiled uniforms.

Harvey had a washing machine and dryer installed inside the warehouse. This allowed the diggers to do their laundry out of sight.

The digging continued for months. Finally, at the end of February 1955, the tunnel had reached the length that had been calculated: 1,476 feet. It was believed to be quite close to the East German telephone cables that were buried, it was believed, 27 inches below ground level, next to a highway.

Royal Engineers

The next step of the operation was to bring in a team of British sappers from the Royal Engineers. These had been practicing their own part of the operation at a base in England. They would dig upwards from the tunnel and try to locate the communication cables. They would then build a small working chamber in which technicians would cut into the cables to place taps.

The exposed tapped telephone cables are exposed to the press. It backfired for the Russians.

As the Royal Engineers got to work, the Americans who had dug the tunnel were put on planes and sent back to military bases in the United States. They were rushed out of Germany as a precaution. The CIA didn’t want the risk of having them in Europe in case they talked about their work.

The British team found the cable and dug out enough room for another British team. These soon arrived, to get to work on the cable itself. In early May 1955 the first of three cables believed to carry Soviet military communications was tapped.

George Blake had tipped off his KGB handlers about the tunnel before it was even dug. But the KGB had a problem using Blake’s information. So few people knew about the tunnel that anything they did to thwart its construction would immediately bring suspicion to Blake.

So the top officers in the KGB decided the best course of action was to keep their astounding intelligence coup to themselves. They didn’t inform the Red Army, and they certainly didn’t inform the East Germans. 

The Discovery

Top generals in the Red Army, as well as soldiers down to the company clerks, kept speaking openly on the telephone lines. The Americans learned the Red Army’s order of battle in Eastern Europe. Loose talk about Soviet officials tipped the Americans off to the location of secret nuclear bases. And when Nikita Kruschev denounced Stalin in his “Secret Speech” in February 1956 the Americans heard about it through loose talk on the telephone lines.

Soviet officers and officials discover the tunnel in 1956

Wires running from the tunnel into the warehouse fed what the Soviets were saying into banks of dozens of Ampex tape recorders. Before long, cartons of tapes were being flown off to Washington to be analysed by CIA linguists. There was so much material being captured that just listening to it all became an enormous challenge.

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By the end of 1955 the KGB, worried about how much information the CIA might be gathering, started making plans to have security officials discover the tunnel. Officials were tasked with doing security checks of the East German telephone system. The security people were never told they were searching for the tunnel.

In the pre-dawn hours of April 22, 1956, a Red Army signals team arrived at the location of the tapped cable. Analysis of telephone traffic on the cable indicated there could be a problem in the area. The location adjacent to the American warehouse along the East-West border seemed to be a likely location to poke around.

Within a day the Soviets had discovered the tunnel. There were no American personnel in the tunnel at the time. The Soviets did not try to transit the entire length of the tunnel.


The top Soviet leadership, especially Kruschev, believed that publicising the tunnel would be a propaganda triumph. Within days the Soviets invited western journalists to climb down into the tunnel. Newspapers published photos of the Soviets showing off their discovery.

A story on the front page of the New York Times on April 24, 1956, noted “The chamber near the Soviet sector end of the tunnel looked like the communications centre of a battleship.”

The propaganda campaign the Soviets were counting on seemed to backfire. In the United States the tunnel, though it had been discovered and shut down, was generally viewed as a triumph. It seemed to indicate to the American public that the American intelligence community was using ingenious means to take on the Soviet Union.

Operation Gold had been blown from the outset, thanks to George Blake. But because the KGB couldn’t exploit his information without revealing him as a source, the tunnel proved to be a success for American and British intelligence. 

The taps on the phone lines had been operational for 11 months and 11 days, according to an internal CIA report. But in that time thousands of unguarded conversations had been recorded and analysed, and there’s no doubt a huge amount of intelligence was gathered.