From the Washington Post, Archives Kept a Secrecy Secret
"The National Archives helped keep secret a multi-year effort by the Air Force, the CIA and other federal agencies to withdraw thousands of historical documents from public access on Archives shelves, even though the records had been declassified.
In a 2002 memorandum, obtained through a Freedom of Information Act request and released yesterday by the National Security Archive, a nonprofit research library housed at George Washington University, Archives officials agreed to help pull the materials for possible reclassification and conceal the identities of anyone participating in the effort. The Associated Press reported yesterday that it had requested a copy of the memo three years ago...
Independent historian Matthew M. Aid uncovered the reclassification program last summer when his requests for documents formerly available at the Archives were delayed or denied. In February, the Archives acknowledged that about 9,500 records totaling more than 55,000 pages had been withdrawn and reclassified since 1999. The memo released yesterday says some records "may have been improperly marked as declassified" and their release "would harm the national security interests of the United States by revealing sensitive sources and methods of intelligence collection."
But historians who previously obtained copies of records have said many date to the 1940s and 1950s and pose no conceivable security risk."