Intelligence Events Timeline
April 19, 2011
CIA released the US Government's six oldest classified documents, dating from 1917 and 1918. The documents describe secret-writing formulas, letter-opening techniques, and methods of covert communications. They are housed at the National Archives and are believed to be the only remaining classified documents from the World War I era. Pictured here, an advanced flaps and seals kit.
No. 107 of 120
![Tools assorted in a tool holder into various pockets.](/static/bd120eae5fc1a6eca1b204ad867059cf/1062d/timeline_041911.jpg)