The CIA’s Oldest Secrets Included Aspirin and Water

Among America’s oldest classified papers was a formula that called for aspirin and pure water. The mixture made invisible ink. The instructions for preparing it and making the writing appear remained unavailable to the public until the government released the documents on 19 April 2011.

The release covered six records dating from 1917 and 1918. The CIA described them as the United States government’s oldest classified documents and believed they were the last remaining classified papers from the First World War. Secret-writing material fell within the agency’s authority to declassify, although the records were housed at the National Archives.

One memorandum, dated 14 June 1918, recorded a German secret-ink formula in French, with an English translation. The National Archives identified it as an Office of Naval Intelligence document. The papers also described techniques for detecting secret writing and opening sealed letters without revealing that someone had examined their contents.

The CIA presented the timing as a technical judgment. Director Leon Panetta said advances in technology had made release possible.

Secret writing had continued to develop after those wartime formulas. In its later account of tradecraft, the CIA described the Cold War shift from liquid inks to dry systems. Soviet services adopted a dry method; the agency’s technical specialists studied and broke such systems. By the Cold War’s end, both sides were using extremely small quantities of chemicals in their messages.

The 2011 release eventually put the old recipes into a public exhibition. From 11 to 31 July, visitors could see the newly declassified material in the National Archives’ East Rotunda Gallery in Washington. The aspirin formula had crossed from protected intelligence paperwork into a free museum display.