Tag Archives: Wullenweber

Paul remembers the FLR-9 “Elephant Cage” in Misawa Japan

Many thanks to SWLing Post contributor, Paul, who writes:

I was a morse intercept operator in the USAF in the late 1960s. I have a nice picture of a FLR-9 at Misawa Japan (now gone I think):

I was at Misawa from 68-70 in the USAF Security Service. I copied high speed code, mostly cut numbers. Got my ham license after discharge. I had 3 R390 receivers at my “position” and numerous different “antennas” on the FLR-9 to listen in different directions. While there I received a commendation for: “Providing information that otherwise would not have been known” I’m not sure I can say any more details.

To me [this photo] shows the immensity of the antenna.

Yes–this antenna is enormous! It must be a site to see up close. I’ve only seen Wullenweber Antennas from satellite imagery. Thank you so much for sharing your photo!

Click here to read previous posts about “Elephant Cages.”

San Diego Elephant Cage scheduled for demolition


On the topic of Wullenweber antennas, SWLing Post reader, Mike, points to this article on U-T San Diego’s website:

Navy’s mysterious ‘elephant cage’ retired: Cold War-era structure a visual landmark on Silver Strand

Beachgoers will say goodbye this month to the “elephant cage” — the mysterious metal structure that has graced the south end of the Silver Strand for 50 years.

The Navy will demolish the circular cage-like contraption as part of an initiative to get rid of obsolete gear.

Officially known as the Wullenweber Antenna Array, the 1,300-foot-diameter structure was built in 1964.

Many details are shrouded in Cold War-era secrecy, Navy officials say.

[…]In simple terms, the huge circular antenna was used to intercept radio signals and detect which direction they came from.

With a range up to 3,200 nautical miles, the Silver Strand antenna likely monitored the Pacific Ocean and parts of Central and South America.

U.S. allies around the world also housed “elephant cages” during the Cold War.

One was located in the United Kingdom, to intercept signals originating from Warsaw Pact nations in Eastern Europe as well as portions of the former Soviet Union.

Another array, located in San Vito dei Norrnanni Air Station. ltaly, opened in 1960 to monitor areas of the Middle East.

Others were built in West Germany, the Philippines, Japan and Canada.

In order to preserve history, the Navy plans to keep the five tallest screens plus some guy wires and anchorage posts. It is also working on a digital 3-D model of the antenna.

Read the full article at U-T San Diego…

Tearing down an Elephant Cage

800px-CDAA_Elmendorf_AFBThis past week, I posted a couple of articles about Wullenweber antennas (a.k.a. “Elephant Cages”). Many thanks to Andrea Borgnino who shares this article by Joseph Trevithick
via Medium.com:

The U.S. Air Force Is Tearing Down a Giant Spy Antenna: ’Elephant cages’ are a dying breed

The U.S. Air Force has started tearing down a massive antenna in Japan. Once used to scan airwaves around the world, these systems have become obsolete as countries change how they communicate.

On Oct. 15, workers began removing the antenna—designated AN/FLR-9—at Misawa air base in Japan. The demolition has been on the flying branch’s agenda for more than a year now.

“Technology and fiscal constraints have driven Misawa Security Operations Center to seek new ways of doing business,” Col. Joseph Winters told Air Force reporters. The antenna—which is almost 1,500 feet wide—should be completely gone by the end of 2015.

Misawa’s system was one of eight AN/FLR-9s the Pentagon built in the United States, Europe and the Pacific during the 1960s. The site actually has three concentric rings of smaller antennae, hence the popular “elephant cage” nickname.

Continue reading on Medium.com…

Mike recalls visiting the original Wullenweber test site


In response to our post Uncovering Wullenweber’s “Elephant Cages,” Mike comments:

Sometime back around 2005-2009, I was doing maintenance on a NOAA climate station near Bondville, IL, and noticed several tall utility poles in the distance. As I figured they looked suspiciously like an antenna array, I asked the site caretaker (it was University of Illinois Champaign-Urbana farm) what they were. He happily took me to see what was left of the original Wullenweber test site, built under contract for the US government for testing by Dr. Hayden. All that remained then was several utility poles, and some transmission line sticking out of the ground.


I’ve also seen the Navy’s array at Imperial Beach, CA (near San Diego), down the highway from the SEAL base, and it’s very impressive. It’s clearly visible from the highway, and though I’ve read it was supposed to come down years ago, its still standing. Makes me wonder if it’s still in use.


Another interesting site I’ve seen is outside of Barrow, Alaska. Near remnants of the DEW Line is a joint USAF/FAA radar station, with a single white domed antenna. I don’t remember exactly, but pretty close to it is what looks to me like a “mini” Elephant Cage. From what I recall, it was a single ring of fairly short towers, surrounding a small central building. When I asked about the facility, I was only told it belonged to an “unnamed agency.”

The first 2 are clearly visible from the following link, while the Barrow site doesn’t stand out enough to be obvious in the Google images.

Click on the “markers” button in the lower right to jump to all the sites: http://tinyurl.com/k5jhxuv

Many thanks, Mike!

Uncovering Wullenweber’s “Elephant Cages”

800px-CDAA_Elmendorf_AFBMany 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.

Click here to continue reading at Gizmodo…

If you’d like to read more about “Elephant Cages” check out the following links: