Operation Gold (also known as Operation Stopwatch by the British) was a joint operation conducted by the American Central Intelligence Agency (CIA) and the British MI6 Secret Intelligence Service (SIS) in the 1950s to tap into landline communication of the Soviet Army headquarters in Berlin using a tunnel into the Soviet-occupied zone. This was a much more complex variation of the earlier Operation Silver project in Vienna.
The plan was activated in 1954 because of fears that the Soviets might be launching a nuclear attack at any time, having already detonated a hydrogen bomb in August 1953 as part of the Soviet atomic bomb project. Construction of the tunnel began in September 1954 and was completed in eight months. The Americans wanted to hear any warlike intentions being discussed by their military and were able to listen to telephone conversations for nearly a year, eventually recording roughly 90,000 communications. The Soviet authorities were informed about Operation Gold from the very beginning by their mole George Blake but decided not to "discover" the tunnel until 21 April 1956, in order to protect Blake from exposure.
Some details of the project are still classified and whatever authoritative information could be found was scant, until recently. This was primarily because the then-Director of Central Intelligence (DCI), Allen Dulles had ordered "as little as possible" be "reduced to writing" when the project was authorized. In 2019, additional specifics became available.
Background
After the Red Army followed the Soviet diplomatic department, and transferred its most secure communications from radio to telephone landline, the post-World War II Western Allies lost a major Cold War source of information. Operation Gold was hence at least the third tunnel built to aid intelligence in the Cold War period post the end of World War II. From 1948 onwards under Operation Silver, British SIS had undertaken a number of such operations in then still occupied Vienna, the information from which enabled the restoration of Austrian sovereignty in 1955. The KGB later commissioned the Red Army to construct a tunnel to tap into a cable that served the major US Army garrison for Berlin.
Operational agreement
In early 1951, the CIA undertook an assessment process for replacing lost Soviet radio communications intelligence. Revealing their plans to the British, the SIS, having read the report which included the idea of tapping Soviet telephone lines, revealed the existence of Operation Silver in Vienna.
On the reassignment of CIA agent Bill Harvey to Berlin to explore available options, Reinhard Gehlen, the head of the Bundesnachrichtendienst, alerted the CIA to the location of a crucial telephone junction, less than underground, where three cables came together close to the border of the American sector of West Berlin. Operation Gold was planned jointly by the SIS and the CIA. Initial planning meetings were held at No. 2 Carlton Gardens, London, from which the West German government were excluded, due to the "highly infiltrated nature" of their service. The resulting agreement was that the US would supply most of the financing and construct the tunnel (as the closest access point was in their sector), whilst the British would use their expertise from Operation Silver to tap the cables and provide the required electronic communications equipment.
One of those who attended the early meetings was George Blake, a mole in the British intelligence apparatus. Blake apparently alerted the KGB immediately, as two of Gehlen's agents were caught trying to get a potential tapping wire across a Berlin canal. The KGB decided to let Operation Gold proceed since, in order to attack the tunnel, the Soviets would have to compromise Blake and they found it preferable to sacrifice some information rather than their valuable agent. According to the author of a 2019 book about the operation, the Soviets "value[d] Blake so much, they fear[ed] his exposure more than they fear[ed] a breach of their secrets".
The KGB did not inform anyone in Germany, including the East Germans or the Soviet users of the cables, about the taps. According to a CIA report, "there were no known attempts to feed disinformation to the CIA". Although the British SIS suspected the opposite, the CIA report states that "the Soviet military continued to use the cables for communications of intelligence value".
Construction
In December 1953 the operation was placed under the direction of William King Harvey, a former U.S. Federal Bureau of Investigation (FBI) official who transferred to the CIA. Captain Williamson of the United States Army Corps of Engineers was placed in charge of construction.