In 2011, the CIA declassified the US Government's six oldest classified documents, dating from 1917 and 1918.
Notes on verification
Confirmed by CIA's own account and multiple independent contemporaneous news reports (NPR, Washington Post) from April 2011. [tier=silver indep_score=0.7 clusters=2 claim_tier=notable | framework convergence=partial (upstreams: CIA declassification action 2011) — publishers independent, evidence may not be | kind=empirical eligibility=high]
Sources
- Secret Writing: CIA's Oldest Classified Documents - CIA (seed:conspiracy_and_investigation)
- https://www.npr.org/sections/thetwo-way/2011/04/07/135227704/cia-declassifies-its-oldest-documents-secret-ink-formulas (corroboration)
- https://www.washingtonpost.com/blogs/checkpoint-washington/post/cia-declassifies-its-oldest-documents/2011/04/07/AFCLwYtC_blog.html (corroboration)