Operation Silver was a British intelligence operation in Allied-occupied Austria which ran from 1949 to 1955 that covertly tapped into the landline communications of the Soviet Army headquarters in Vienna.
[1] Staff included Peter Lunn, Peter Montagnon, Major John Edward Wyke of the SIS and telecommunication specialists from the BPO Research Station at Dollis Hill.
[2] Although the operation was considered a success, the details of it were passed on to the KGB in October 1953 by George Blake, a British double agent.
[3] The British monitoring station was disguised as a shop that sold tweed clothing.
Blake had also informed the Soviet authorities about Operation Gold in its very beginning, and they "discovered" the tunnel in 1956.