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Executive Order 13526
The US executive order governing the classification of national security information. It is referenced throughout PURSUE Release 01, both on military documents and on State Department cables.
Section 1.4(a), the code seen most often in the release, covers military plans, weapons systems and operations. Redactions citing 1.4(a) hide operational detail. Personnel identities are redacted separately, under Freedom of Information Act exemptions (b)(6) and (b)(3). The pattern matters: in the PURSUE documents the redaction codes mark operational and personnel secrecy, not the UAP observation itself, which is usually left visible.
Document briefings
Briefing 01, what is inside PURSUE Release 01 · Briefing 06, the Mexico City diplomatic cable · Briefing 07, an F-15E over Syria