Many thanks to SWLing Post reader, Bill Patalon, for sharing this article via Gizmodo:
In the early days of electronic espionage, the US intelligence community didn’t have the benefit of all-seeing spy satellites—it had to intercept and interpret high-frequency radio waves transmitted by the Soviet Union. To do so, the Americans relied on a network of mysterious structures whose real purpose was kept highly classified throughout the Cold War.
Nicknamed “Elephant Cages” by outside observers, these structures were actually high-frequency antenna arrays, part of the US military’s AN/FLR-9 “Iron Horse” system. These arrays, commonly known as “Wullenweber” antennas—and named after German WWII scientist, Dr. Hans Rindfleisch was Wullenwever—are a type of Circularly Disposed Antenna Array (CDAA). They can be used for a variety of purposes from intelligence gathering and identifying high-value targets to navigation and search and rescue operations.
Each elephant cage consisted of an inner ring of antennas tuned for high frequency waves surrounded by one or more outer rings tuned for lower frequencies. These antennas would listen for HF radio waves bouncing off the ionosphere (which is what also allows HF radios to communicate beyond the horizon) and triangulate the precise location of the signal’s source.
If you’d like to read more about “Elephant Cages” check out the following links: