This summer, reporting based on documents disclosed by Edward Snowden gave an indication of the extent of German cooperation with NSA surveillance. In particular, Der Spiegel’s reporting drew attention to the involvement of Germany’s BND in the NSA’s corporate partnerships and the agencies’ jointly staffed projects based at Bad Aibling in Bavaria.
This undated document lists the locations of US-operated signals intelligence stations in Germany (some have been redacted): see the Der Spiegel article The NSA in Germany: Snowden’s Documents Available for Download, 18 June 2014.
This internal NSA post from 16 September 2003 describes one agency staffer’s experience of working at the NSA’s German stations: see the Der Spiegel article Spying Together: Germany’s Deep Cooperation with the NSA, 18 June 2014.
A listing of Sigads (Signals Intelligence Activity Designators, or collection stream associated with a signals intelligence station) based in Germany, collated by Der Spiegel. For around a dozen of the 150 or so historical sigads in this list, no closing date is supplied: see the Der Spiegel article Snowden-Dokumente: Hier sitzt die NSA in Deutschland, 18 June 2014.