Operation Gold was a joint operation conducted by the American Central Intelligence Agency (CIA) and the British 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. The Berlin Tunnel was a major engineering feat. It stretched 1476 feet/454 meters through sandy ground to reach a cable only 27 inches/68.5 cm beneath the surface, on the edge of a major highway. One of the most difficult engineering problems that had to be overcome in the course of the project was to dig up to the cable from the main tunnel shaft without dropping some truck passing over the highway above into the tunnel. During the night of 21-22 April 1956, the Soviets discovered the tunnel, and collection ceased. That did not close the project, however. The take from the Berlin Tunnel during the time that it was operational (11 months and 11 days) was so great that processing of the backlog of material continued through the end of September 1958. Details of the project are still classified-especially by the British-and whatever authoritative information can be found is scant. This is primarily because the then-Director of Central Intelligence (DCI), Allen Dulles ordered "as little as possible" be "reduced to writing" when the project was authorized. The Berlin Tunnel episode illustrates how elements of success and failure can be found in the same intelligence operation. The cable taps yielded enormous amounts of intelligence on a hard target and answered important strategic questions for US policymakers and war fighters. The success in numbers includes: - 50,000 reels of tape - 443,000 fully transcribed conversations (368,000 Soviet and 75,000 East German) - 40,000 hours of telephone conversations - 6,000,000 hours of teletype traffic - 1,750 intelligence reports Subsequent studies determined that the Soviets had not attempted to feed false information over the tapped lines-the intelligence that had been collected was genuine. Despite the KGB's foreknowledge, CIA ruled this most ambitious operation a success-it yielded valuable intelligence for US policymakers and war fighters, including: - Detailed order of battle and information on activities of Soviet and Warsaw Pact forces - Identification of people working on Soviet atomic energy projects - Early warning of the Soviet's establishment of an East German army - The poor condition of East German railways - Resentment between Soviets and East Germans - Great tension in Poland - Soviet inaction regarding a military invasion of Western Europe. The intelligence fame/obscurity paradox aside, the Berlin Tunnel operation was, in the words of Allen Dulles (then DCI), "one of the most valuable and daring projects ever undertaken" by the CIA.