This NSA classification guide, dated 21 November 2011, covers signals intelligence material that as to be kept secret for more than the standard 60 years: see the Der Spiegel article The NSA in Germany: Snowden’s Documents Available for Download, 18 June 2014.

This undated internal NSA document illustrates the degrees of cooperation in the agency’s relationships with different foreign powers. “Tier A” and “Tier B” are elsewhere referred to as Second and Third Parties: see the book No Place To Hide, 13 May 2014.

NSA is training staff at Hungary's Military Intelligence Office (MIO) to write signals intelligence reports for dissemination to the NSA system. MIO provides unique access to Serbian and Ukrainian military targets and expertise that helps fill the NSA's gaps.

This 24 February 2005 article from the internal NSA newsletter Foreign Affairs Digest describes third party cooperation and interoperability in High Frequency Direction-Finding (HFDF): see the Intercept article Japan Made Secret Deals With The NSA That Expanded Global Surveillance, 24 April 2017.

This slide, taken from the NSA’s annual report on the state of its cooperation with foreign powers, details the countries that have received payments from the agency: see the book No Place To Hide, 13 May 2014.

This slide, taken from the NSA’s annual review of its cooperation with foreign partners, shows an expansion in the agency’s international relationships: see the book No Place To Hide, 13 May 2014.

The U.S. closed a number of High Frequency Direction-Finding sensor sites in the 1990s. To ensure they're able to track signals in areas that had previously been covered by now-shuttered stations, the Signals Intelligence Directorate worked with Second and Third Party partners to share resources and establish a global direction-finding network.

An NSA couple worked at locations in Germany’s Rheinland and enjoyed local cuisine and European travel.