German Secret Ink
6/14/1918
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For 95 years, a small number of documents related to invisible ink were national security-classified material and unavailable to the public. Believed to have been the oldest documents still classified by the United States, they detail German secret ink formulas developed during World War I. They were approved for release in the year 2011. This document is a copy of the formulas, written in French, used in preparation of German secret ink.
This primary source comes from the Records of the Office of the Chief of Naval Operations.
National Archives Identifier: 5890788
Full Citation: German Secret Ink; 6/14/1918; File 20961:174; Records of the Office of the Chief of Naval Operations, Record Group 38; National Archives Building, Washington, DC. [Online Version, https://www.docsteach.org/documents/document/german-secret-ink, April 24, 2024]Rights: Public Domain, Free of Known Copyright Restrictions. Learn more on our privacy and legal page.