The Mysterious “Elephant Cage” of Imperial Beach
San Diego’s Giant Cold War Listening Station
Greg Ross
CEO / Owner - Nancy's Vacation Rentals
For decades, an enormous circular structure towered over the southern end of San Diego Bay. Locals called it the “Elephant Cage.” But there were never any elephants inside. What happened there was considerably more interesting.
If you lived in San Diego's South Bay before 2015—or drove the Silver Strand between Coronado and Imperial Beach—you may remember seeing something very strange near the southern end of the peninsula.
From a distance, it looked almost impossible to identify.
Dozens of enormous poles formed a gigantic circle.
Between them stretched an elaborate web of antennas, cables and wires.
It looked a little like a fence.
A little like a giant circular cage.
And perhaps a little like something the government wasn't particularly interested in explaining.
Locals gave it an appropriately mysterious nickname:
The Elephant Cage.
But this wasn't a zoo.
It was part of a sophisticated military system designed to listen for radio signals and determine exactly where they were coming from.
And during the Cold War, that made the strange structure sitting beside Imperial Beach an important piece of America's electronic intelligence network.
First Things First: There Were No Elephants
Despite its name, the Elephant Cage had absolutely nothing to do with animals.
The nickname came from its appearance.
Its real name was considerably less catchy:
AN/FRD-10 Circularly Disposed Antenna Array.
It was a type of antenna generally known as a Wullenweber array.
These enormous circular antenna systems were constructed at military installations around the world. Their purpose was radio direction finding—identifying the direction from which distant radio transmissions originated.
The giant reflecting screens surrounding some of these installations resembled enormous circular fences.
Hence the nickname:
Elephant Cage.
San Diego's Military Radio History Started Much Earlier
The story actually begins decades before the Elephant Cage appeared.
The Navy established a Radio Compass Station in the area in 1920.
Its job involved radio navigation and direction finding—a technology that was becoming increasingly important to ships operating offshore.
By 1940, the installation had become the Navy Direction Finder Station.
Then World War II changed everything.
Radio signals weren't simply useful for navigation anymore.
They were intelligence.
Knowing where an enemy transmission originated could help reveal the location of ships, aircraft and military units.
The quiet stretch of coastline between Imperial Beach and Coronado became part of America's rapidly expanding signals-intelligence operation.
The Women Who Listened During World War II
There's another fascinating piece of the site's history that deserves considerably more attention.
During World War II, members of the Navy's WAVES — Women Accepted for Volunteer Emergency Service — were stationed at the direction-finding facility.
Thirty WAVES were reportedly stationed there in 1943.
By 1945, that number had grown to 112 women.
Their work included signals intelligence.
Think about that for a moment.
While battles were raging across the Pacific, young women were sitting along this relatively isolated stretch of San Diego coastline listening to and analyzing radio transmissions.
Today we tend to associate intelligence gathering with satellites, computers and sophisticated digital surveillance.
During World War II, radio operators with headphones and direction-finding equipment could provide extraordinarily valuable military intelligence.
Then the Cold War Arrived
After World War II ended, another geopolitical struggle began.
The United States and Soviet Union entered the Cold War.
And once again, radio communications became extraordinarily important.
Submarines moved beneath the oceans.
Soviet ships operated throughout the Pacific.
Military aircraft crossed enormous distances.
Radio signals traveled through the atmosphere.
And if you could determine where those signals originated, you could learn an enormous amount about what another military was doing.
That's where the Elephant Cage came in.
In 1965, Imperial Beach Got Its Giant Cage
By 1953, the installation was known as the Naval Radio Receiving Facility Imperial Beach.
Then, in 1965, the Navy installed the massive Wullenweber circular antenna that would become the site's defining landmark.
Imagine seeing it appear for the first time.
A huge circle of towers and antennas rising from an otherwise relatively flat coastal landscape.
From above, it looked almost like a giant mechanical crop circle.
From the ground, it resembled an enormous fence.
And from the Imperial Beach Pier, its strange circular silhouette could be visible to the north.
So What Did the Elephant Cage Actually Do?
Here's where things get interesting.
The Elephant Cage was essentially an enormous radio direction finder.
Suppose a ship hundreds or even thousands of miles away transmitted a radio message.
The Imperial Beach antenna array could receive that signal.
Because antennas surrounded the entire circle, operators could analyze the incoming signal and determine the direction from which it originated.
Combine that information with direction-finding information from another station and something extremely powerful became possible:
Triangulation.
If one station determined that a signal came from one direction and another station detected that same transmission from another direction, analysts could estimate where those lines intersected.
And suddenly a radio transmission had a location.
The system could support radio direction finding, navigation, intelligence gathering and search-and-rescue functions.
Imagine a Soviet Ship Somewhere in the Pacific
Here's a simplified example.
Imagine it's 1975.
Somewhere in the Pacific, a Soviet naval vessel transmits a radio message.
The crew might be hundreds or thousands of miles from San Diego.
They can't see California.
San Diego can't see them.
But radio waves don't care about the horizon.
The transmission travels through the atmosphere.
The Elephant Cage detects it.
Operators analyze the signal.
Another military station receives the same transmission.
Combine the directional information from multiple stations and intelligence analysts can begin determining where that transmitter is located.
You don't necessarily have to understand what someone is saying to learn something useful.
Sometimes simply knowing who is transmitting, when they're transmitting and where they're transmitting from can reveal valuable information.
Why Build It Near Imperial Beach?
The location made a lot of sense.
Southern San Diego sits beside an enormous expanse of the Pacific Ocean.
The area also already had a long history of Navy communications operations.
And San Diego had become one of America's most important naval centers.
From the Elephant Cage's position near the southern end of the Silver Strand, military operators had an ideal coastal location for monitoring radio signals traveling across the Pacific.
Was It Secret?
This is where the story needs a little restraint.
It's tempting to describe the Elephant Cage as a “secret spy base.”
That makes a fantastic headline.
It's also not quite accurate.
The structure itself was virtually impossible to hide.
It was gigantic.
Residents could see it.
People driving Highway 75 could see it.
Beachgoers could see it.
You could even spot it from the Imperial Beach Pier.
Its general radio-direction-finding purpose was eventually well understood.
What ordinary residents generally wouldn't have known were the details of particular military intelligence operations and exactly what signals were being collected or analyzed.
So rather than being a completely secret facility, it was something arguably more intriguing:
A highly visible military intelligence installation whose exact day-to-day activities weren't necessarily visible at all.
The Name “Wullenweber” Has an Even Stranger History
The technology itself predates the Imperial Beach installation.
Circular radio direction-finding arrays were developed in Europe before and during World War II, and “Wullenweber” became associated with this style of antenna.
After the war, the United States and other nations developed increasingly sophisticated versions of the technology.
During the Cold War, similar giant circular antenna arrays appeared at military installations around the world.
Some became local landmarks.
Many acquired the same nickname:
Elephant Cages.
Imperial Beach happened to have one sitting practically beside the Pacific Ocean.
Then Technology Passed It By
Like many extraordinary Cold War technologies, the Elephant Cage eventually became obsolete.
Satellites, improved electronic surveillance systems, newer antenna technology and increasingly sophisticated digital communications changed how signals intelligence was collected.
The Navy's Imperial Beach Wullenweber ceased operating in 1999.
But something strange happened.
The Elephant Cage didn't immediately disappear.
It just sat there.
For years.
The enormous circular structure remained a familiar South Bay landmark long after it had stopped performing its original mission.
If you didn't know what it was, it became even more mysterious.
For Years, San Diegans Drove Past a Cold War Relic
By the early 2000s, the Elephant Cage had become something of an accidental historical monument.
People drove past it on the Silver Strand.
Cyclists saw it.
Beachgoers wondered about it.
Visitors standing on the Imperial Beach Pier could look north and ask the inevitable question:
“What in the world is that?”
But the structure's days were numbered.
The Elephant Cage Comes Down
By 2014, the Navy was preparing to remove the aging Cold War landmark.
In 2015, the Elephant Cage was dismantled.
After approximately half a century dominating the landscape, the enormous circular antenna disappeared.
Today, someone driving through the area for the first time would have little reason to suspect it ever existed.
But the military story of the property didn't end.
Quite the opposite.
From Cold War Listening Station to Special Operations Training
The former radio-receiving property became part of today's Silver Strand Training Complex, associated with Naval Base Coronado.
Its mission changed dramatically.
Instead of listening for distant radio transmissions, the roughly 450-acre facility became a major training environment used by U.S. military special operations forces.
Its geography is particularly useful.
The property sits between the Pacific Ocean and San Diego Bay, allowing waterborne approaches from both sides.
The site also includes training areas that can support urban-style military exercises.
So one of San Diego's great Cold War communications sites eventually became part of an entirely different generation of military training.
Wait — Is It Actually in Imperial Beach?
Here's a geographical technicality worth clearing up.
Everyone calls it the Imperial Beach Elephant Cage.
The Navy itself historically used “Imperial Beach” in names associated with the radio facility.
And it sits immediately beside Imperial Beach.
But the site is actually on the Imperial Beach/Coronado border, within Coronado's municipal boundaries.
That's one of those wonderfully confusing San Diego geographical details.
For generations of South Bay residents, though, it was simply:
The Elephant Cage.
Can You See the Elephant Cage Today?
Unfortunately, no.
The famous circular antenna structure was dismantled in 2015.
The property remains an active military installation, so this isn't an abandoned Cold War site you can wander around exploring.
But you can still appreciate the location from the surrounding South Bay and Silver Strand area.
And if you happen to have an old photograph taken north from Imperial Beach, look carefully in the distance.
You may discover that enormous circle of poles hiding in plain sight.
The Giant Structure San Diego Almost Forgot
That's what makes the Elephant Cage such a perfect piece of San Diego history.
For approximately half a century, this enormous structure stood beside one of Southern California's most populated metropolitan areas.
Millions of people probably saw it.
Most had no idea what it actually did.
It quietly witnessed the Cold War.
It listened across the Pacific.
It supported a military communications and intelligence mission few beachgoers thought about while looking north from the Imperial Beach Pier.
Then one day it disappeared.
Today, there's an entirely new generation of San Diegans who will never remember seeing it.
But for anyone who grew up in the South Bay during the second half of the 20th century, the silhouette is difficult to forget.
A gigantic circular cage beside the Pacific Ocean.
No elephants. Just antennas.
And one remarkable piece of San Diego's Cold War history.
Frequently Asked Questions
What was the Elephant Cage in Imperial Beach?
The Elephant Cage was an enormous Wullenweber circular antenna array at the Naval Radio Receiving Facility near Imperial Beach. It was primarily used for radio direction finding and military communications and intelligence functions.
Were there really elephants there?
No. “Elephant Cage” was a nickname given to large circular antenna arrays because their giant reflecting screens and surrounding structures resembled enormous circular cages.
When was the Imperial Beach Elephant Cage built?
The large Wullenweber circular antenna array was installed in 1965.
Was the Elephant Cage used to spy on the Soviet Union?
Its radio-direction-finding technology was useful for signals intelligence during the Cold War. However, claims about specific intercepted Soviet communications should be treated carefully unless supported by declassified operational records.
When did the Elephant Cage stop operating?
The Navy's Wullenweber array ceased operation in 1999.
When was the Elephant Cage demolished?
The massive circular antenna structure was dismantled in 2015.
What's there today?
The area is now part of the Navy's Silver Strand Training Complex, a military training facility associated with Naval Base Coronado.
San Diego's Strangest Stories Are Often Hiding in Plain Sight
We tend to think of San Diego history in terms of missions, beaches, Balboa Park and famous landmarks.
But some of the city's most fascinating stories aren't marked by monuments.
They're places thousands of us drove past without realizing what we were looking at.
At Nancy's Vacation Rentals, we've spent more than 25 years helping visitors experience San Diego's beach communities.
Our San Diego Uncovered series explores the forgotten landmarks, strange history and local stories that reveal an entirely different side of America's Finest City.
Because sometimes the most interesting question you can ask about San Diego is simply:
“What used to be here?”
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For decades, a mysterious giant circular antenna known as the Elephant Cage towered near Imperial Beach. Discover how this massive Cold War Navy installation listened for and located radio signals across the Pacific.
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