Roaming the CIA pages always provides something interesting, in this case I found a list of documents that throw a light on the expionage methods in WWI as employed by the US Office of Naval Intelligence
The documents (two written in French) detail e.g. how Tatoos can be made visible (or your own invisible), how the Germans made invisible ink, how to make your own, or how to open sealed letters without getting found out.
Because of "recent" advancements in technology (according to CIA Director Panetta) the CIA felt it was finally ok to declassify those documents after almost 100 years, they were up to now the oldest classified stuff the agency held, as Intelligence bureaucrats believed for decades that these long outmoded tools of the spy trade needed to be kept out of the public purview. One of them carries a stamp from 1978 marking it “EXEMPT from automatic declassification.” The one with the invisible tattoos has a different non-disclose stamp from 1989.
Enjoy!
Rattler
