The U.S. Central Intelligence Agency on Wednesday declassified the government's six oldest classified documents, dating from 1917 and 1918.

These documents, which describe secret writing techniques, are housed at the National Archives, and are believed to be the only remaining classified documents from the World War I era. Documents describing secret writings fall under the CIA's purview to declassify.

These documents remained classified for nearly a century until recent advancements in technology made it possible to release them, CIA Director Leon E. Panetta said. When historical information is no longer sensitive, we take seriously our responsibility to share it with the American people, it said.

One document outlines the chemicals and techniques necessary for developing certain types of secret writing ink and a method for opening sealed letters without detection. Another memorandum dated June 14, 1918 - written in French - reveals the formula used for German secret ink, it added.

The CIA recognizes the importance of opening these historical documents to the public, said Joseph Lambert, the Agency's Director of Information Management Services. In fiscal year 2010 alone, the Agency declassified and released over 1.1 million pages of documents.

The documents will be available on and in the CIA Records Search Tool (CREST) at the National Archives in College Park, Maryland. CREST currently houses over 10 million pages of declassified Agency documents. Since 1995, the agency has released over 30 million pages as a result of Executive Orders, the Freedom of Information Act (FOIA), the Privacy Act, and mandatory declassification reviews.