The project is described as:The FBI has been hiding sensitive records of American eavesdropping operations from parliamentary scrutiny for decades. FBI director J. Edgar Hoover (right) gave orders in 1948 for tricky political papers to be stored away in Room 6527 – known as the Confidential File Room - at its Washington headquarters. The records did not show up in any index so that the FBI would be able to deny any knowledge of the relevant documents should a parliamentary control commission ever start to ask questions.
Along with records of US eavesdropping on friendly states, Hoover also stashed away documents about Eastern Block spies or reports about the unusual sexual practices of senior Communist officials and politicians. There were so many documents that they began to threaten the vast official building’s structural mechanics. An internal FBI memo from September 1961 notes that secret papers had to be immediately transferred to other rooms due to the weight of Room 6527’s 26 filing cabinets. Thanks to a Freedom of Information Act request, the SonntagsZeitung and Le Matin Dimanche have gained access to these historic and previously unpublished intercept records.
Regarding the available files I had a quick look and the pdf ‘diplomatic code Greek’, pages 5-23 has a summary of AFSA (predecessor of the NSA) efforts versus the codes of Eastern European countries in the 1950’s. Very interesting stuff!