The U.S. Air Force had two ground-based signals intelligence intercept sites at Da Nang, South Vietnam -- one at the air base and another, pictured here, on nearby “Monkey Mountain” (Sơn Trà Mountain).
NSA
<a rel="nofollow" class="external text" href="http://www.nationalmuseum.af.mil/photos/index.asp">National Museum of the U.S. Air Force</a> photo <a rel="nofollow" class="external text" href="http://www.nationalmuseum.af.mil/shared/media/photodb/photos/2014%5C01%5C140114-F-DW547-013.jpg">140114-F-DW547-013</a>