Newly declassified documents detail the CIA’s secret Cold War spy-pigeon missions, the BBC reported Saturday.

The files reveal how pigeons were trained for clandestine missions photographing sensitive sites inside the Soviet Union, according to the BBC.

The 1970s operation was codenamed “Tacana” and explored the use of pigeons with tiny cameras automatically taking photos.

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On its website, the CIA said the collection of declassified documents highlight the diverse programs involving the feasibility of using dolphins and birds to support spying operations.

“For a variety of technical and other reasons, none of the programs ever became operational,” the CIA said.

The CIA flew pigeon test missions in the mid-1970s, including one over a prison and another over the Navy Yard in Washington, according to the BBC report.

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The pictures taken over the Navy Yard with a camera that cost $2,000 showed remarkably clear details of people walking and cars parked, the broadcaster reported.

As it conducted the tests, the CIA feared a member of the public stumbling upon a camera-equipped pigeon so spymasters devised an elaborate cover story, according to the BBC.

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A September 1976 memo shows the CIA selected a Leningrad shipyard where the most advanced Soviet subs were being built as an Operation Tacana target.