The Mullingar-born singer, who died on December 26th last year, attracted the attention of the Army intelligence branch, G2, when he agreed to perform in Moscow at the height of the Cold War in 1978.
In one of its secret files are several newspaper cut-outs with photographs of the singer's time in the former USSR, where he played 23 concerts over 23 nights in Moscow, Leningrad and Kishinev, the capital of Moldova.
In one of the articles, the apolitical singer tells an interviewer how the Soviet audiences knew all his hits, and even "went wild about the Westmeath Bachelor".
The documents were only declassified earlier this month by the Defence Forces' director of intelligence so they could be released into the National Archives under the 30-year rule.
There is no other supporting evidence in the top-secret file of any alleged communist activities by the popular crooner, best-known for hits like Make Me An Islandand You're Such A Good-Looking Woman.