DoD used 80 towers and 400-meter arrays to pin targets 5,000 kilometers away
By Marcus Boone ·
Local populations were left to guess the purpose of massive antennae that sparked panic and fears of secret missile bases among British communists.
The image is unmistakable: a massive, circular tangle of wire and steel that looks less like a piece of military hardware and more like a discarded industrial accident. They were popularly known as "elephant cages," a name born from a joke by a non-commissioned officer at Misawa Air Base in 1964 who told curious onlookers that the structures were designed to keep elephants from running loose. In reality, the AN/FLR-9 was a primary tool of the Department of Defense World Wide High Frequency Direction Finding System, designed to snatch radio signals out of the ionosphere and pin a transmitter's location on a map.
According to a program page from the FAS Intelligence Resource Program, the AN/FLR-9 functioned by detecting the "line of bearing" of a radio transmitter. When two or more of these stations picked up the same signal, the intersection of those lines marked the target's location. The scale was immense. A typical site featured a horizontal ground screen roughly 400 meters in diameter, with two rings of antennae—an inner ring of about 230 meters and an outer ring of about 260 meters—supported by 80 towers. These arrays could reach out between 150 and 5,000 kilometers, turning the sky into a giant reflector for the Air Intelligence Agency.
"They work pretty well, don't they"
This network, codenamed "Iron Horse," was rolled out across the globe in the early 1960s. The first sites were equipped at San Vito in Italy and Chicksands in England. Others followed at Misawa in Japan, Clark in the Philippines, and Elmendorf in Alaska. The system didn't just appear; it was a massive engineering undertaking that relied on a specialized workforce. The operations side was populated by Morse Intercept operators, Radio Telephone operators translating foreign voices into English, and "202" Radio Intercept Analysis Specialists.
One former specialist, David Michael Wade, recalls serving at the site outside Brindisi, Italy, between 1962 and 1964. Wade described himself during that tour as a "titless WAF," noting that all the operations personnel—the 292s, 203s, and 202s—were men. The secrecy surrounding these sites was absolute, yet the structures were too large to truly hide. The government's solution was to let the local populations guess, or to provide thin covers that often spiraled into panic.
Document imagery from irp.fas.org From the files: irp.fas.org
San Vito and the Honey Wagon
At the Chicksands site in England, the vertical antennae resembled Redstone missiles. This visual similarity sparked a rumor within the British Communist Party that the U.S. was building a secret missile base on British soil. A protest march was in the works until, as the record notes, someone—likely the KGB—informed the organizers of the site's actual purpose as a listening post, and the rally was called off.
In Italy, the secrecy was matched only by the incompetence of the site's logistics. An engineer named Bob Ney recalls a design flaw at San Vito where two septic tanks were buried directly on top of a quiescent artesian spring. During the rainy season, the concrete covers of the tanks simply floated to the surface. When a local "honey wagon" arrived to pump the tanks, the truck bogged down in the mud. A D-8 Cat wouldn't start, and a tank recovery vehicle was too tall to fit through the gate of the HF array. The driver eventually opened the valves on the truck, leaving the central building in a state where getting to work was, for a week, a "hold-your-breath-and-run" event.
Document imagery from irp.fas.org From the files: irp.fas.org
18 Megahertz to 30 Megahertz
Technically, the AN/FLR-9 was an evolution of the Wollen-Weber antenna, a design used by the German Navy to communicate with submarines during World War II. The U.S. version expanded this into a full 360-degree surveillance tool. The array used various elements—folded dipoles, sleeve monopoles, and bow tie antennae—to cover different bands of the spectrum, from 3 MHz up to 30 MHz.
While the system was designed for permanence, it remained vulnerable to the environment. A site south of Homestead Air Force Base in Florida, operated by the Naval Security Group, was a point of contention in the FAS records. While one contributor claimed the site was an AN/FLR-9, another corrected the record, identifying it as a Navy AN/FRD-10. Regardless of the model, the site's end was absolute. During Hurricane Andrew in 1992, the antenna system didn't just break; a crew returning to the site found that the storm had "completely blew it out to sea." Not a single pole, wire, or element remained.
With the arrays gone or rendered obsolete by solid-state preamplifiers and newer technology, the record leaves the final fate of many of these "elephant cages" vague. At Homestead, after four days without power and the total erasure of the array, the decision was made not to reopen the site.