The tunnel ran 1,476 feet from a U.S. Air Force radar site in West Berlin to Soviet communication lines on the far side of the sector border. For 11 months it fed Western intelligence a stream of Soviet military conversations. The catch, as the CIA tells it, is that the KGB knew about the operation while it was still being planned, and the tunnel paid off anyway.
The CIA has told the story of Operation GOLD on its own website, and its account answers the obvious question: how could a compromised operation still produce intelligence the agency considers genuine?
In a story published April 19, 2024, the CIA lays out the joint operation it ran with Britain’s MI-6. Berlin was the target because, the agency writes, “Almost all of the communications between Moscow (Russia), Warsaw (Poland), and Bucharest (Romania) went through Berlin.”
A warehouse, a radar site and 3,100 tons of sand
“In January 1954, then-CIA Director Allen Dulles approved the covert tunneling and tapping operation,” the CIA writes. The cover was mundane by design: “The CIA used a U.S. Air Force radar site and warehouse in West Berlin as cover for the construction of the tunnel.”
The digging was a heavy-construction job carried out in secret. According to the agency, “Tunnelers removed 3,100 tons of soil.” Berlin’s ground was a hazard of its own. “The soil was quite sandy, so to avoid potential cave-ins, technicians decided that the tunnel should be lined with steel,” the CIA says, describing a lining built from steel rings approximately six feet in diameter.
“Construction took a year,” the agency writes. “The finished tunnel was 1,476 feet long—roughly the length of the Reflecting Pool in front of the Lincoln Memorial.” Then the British side took over the delicate part: “British technicians installed the taps, and collection began on May 11th, 1955.”
The mole inside MI-6
The operation had been betrayed before construction began. “George Blake, a KGB mole inside MI-6, had told the Soviets about the secret operation during its planning stages,” the CIA writes, and the KGB “had been aware of the project from its start.”
The Soviet service faced a choice between stopping the tunnel and protecting its source. According to the agency, it chose the source: “to protect Blake, the KGB allowed the operation to continue until April 21, 1956 (April 22 in Berlin).”
The CIA’s account of the ending turns on the weather. “The spring season had been exceptionally rainy, causing many short circuits in Berlin’s telephone network,” it writes. A team of Soviet and East German soldiers began digging at a municipal cemetery in Altglienicke, East Berlin, and found that the cable had been wiretapped and rerouted into a secret tunnel, per the agency. The CIA says the Soviets planned the discovery “in hopes of winning a propaganda victory by publicizing the operation,” but that “most press coverage marveled at the audacity and technical ingenuity of the operation.”
443,000 conversations, and why they held up
The harvest is where the story turns. The CIA lists the tunnel’s output as “443,000 fully transcribed conversations” and “1,750 intelligence reports.” It adds: “Following the tunnel’s shutdown, processing of this immense volume of data took more than two years to complete.”
On the question at the heart of the operation, whether the KGB fed the West false material, the agency’s answer is measured: “The intelligence collected, as far as CIA can tell, was genuine.” The agency also writes that “historians consider the Berlin Tunnel one of the greatest intelligence successes of the Cold War.”
What is left of it
Pieces of the tunnel survive in Berlin. The AlliiertenMuseum’s page on its espionage-tunnel exhibition says the museum has owned a restored tunnel segment since 1997, now in its permanent exhibition. It describes the tunnel as running about 450 meters, the same length as the CIA’s 1,476 feet, from Neukölln/Rudow in the American sector to Treptow/Altglienicke in the Soviet sector.
The museum’s figure for the haul is rounded but close to the CIA’s: “Some 440,000 telephone calls were recorded” over the 11 months before Soviet army units uncovered the tunnel in April 1956. For the special exhibition marking the tunnel’s 50th anniversary in 2006, the museum also recovered what it calls the “last authentic piece” of the tunnel, working with Berlin’s ministry for urban development in 2005.
Top image: A surviving section of the Berlin spy tunnel on display at the AlliiertenMuseum in Berlin. Image Credit: Anagoria — CC BY 3.0 / Wikimedia Commons