The Mount Alto Tunnel is the eavesdropping tunnel the FBI and the National Security Agency are reported to have dug beneath the Soviet, now Russian, embassy compound on Mount Alto, at 2650 Wisconsin Avenue NW. Its existence became public on 4 March 2001, when the New York Times reported that officials believed it had been betrayed to Moscow by Robert Hanssen, the FBI agent arrested as a spy two weeks earlier. The affidavit against Hanssen said he had compromised an entire technical program of enormous value, expense and importance, and officials told the Times that this meant the tunnel.
The compound stands on the site of the old Mount Alto veterans' hospital. The Soviet Union signed an 85-year lease on it in 1969, construction began in 1977, and Soviet diplomats moved into its apartments in 1979. The tunnel and related operations were reported to have cost several hundred million dollars, and former officials doubted it ever produced useful intelligence. The government has never acknowledged it. Asked on television the day the story broke, Vice President Dick Cheney said that if such a tunnel had been dug, he could not talk about it anyway.
Hanssen, who had volunteered to Soviet intelligence in 1985, pleaded guilty, was sentenced to life and died in prison in 2023. The tunnel's entrance has never been identified, though a house across Wisconsin Avenue has long been rumoured to be an FBI watch post.
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38.9246, -77.0748
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