Operation Gold was a joint operation conducted by the American CIA and the British Secret Intelligence Service 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.

The covert construction of a 1,476-foot tunnel twenty feet under the world’s most heavily patrolled border to intersect a series of cable less than eighteen inches below a busy street was an exceptional engineering challenge. Work began in August, 1954 and was completed on 25 February the following year.

The tunnel entrance was concealed as a new CIA radio intercept site. Spoil was stored in warehouses built for the purpose. The intercepts were not decoded, but were read in plain text due to an electronic echo produced by the Soviet equipment.

Interestingly, the Soviets knew of the tunnel due to George Blake, a “mole” in the British intelligence apparatus. To protect this operative, and thinking their codes were secure, the Soviets allowed the tunnel to operate until 21 April, 1956. when the tunnel was dramatically "discovered" by an outraged Soviet commander who showed it to the world’s press.

Directly under the border was a steel door marked “Entry Forbidden by the Commanding General.” The tunnel was hailed throughout the Free World as an engineering triumph. It was called Operation Stopwatch in British documents.

Operation Gold was also the codename for support of the 2000 Summer Olympics in Sydney by the Australian armed forces . The military provided aviation, security and explosive ordnance disposal units to help the games run smoothly.