Extremely Low Frequencies

The submarine is a surprisingly ancient technology—at least in its early, primitive forms. The idea is quite simple, that a well-enough-sealed boat ought to be able to submerge and resurface. It's the practicalities that make the whole thing difficult. It is generally considered that the US Civil War was the first use of submarines in combat; these were primitive machines with very limited operating endurance and navigational capabilities. These submarines were more like torpedoes: you pointed them in the right direction and hoped they went straight.

The First World War benefited from tremendous advances in submarine technology. A number of experimental designs during the 19th century had built practical experience, especially in Germany, and the Germans apt use of the first modern "U-boats" had a significant military impact. British and US designs made similar advances, and submarine warfare was born.

The chief advantage of the submarine is its ability to submerge and maneuver while hidden. WW1 submarines were diesel-electric or gasoline, so their submerged endurance was limited by the power supply stored onboard. Still, these submarines could operate underwater longer than any before, long enough to establish the submarine sneak attack as a key part of naval warfare.

It was also long enough to expose one of the trickiest challenges of underwater defense: communications. Water, especially seawater, is dense and conductive. This is very bad for radio wave propagation: by the first world war it had already been discovered that seawater effectively blocked radio communications. HF radio, the main form of communications at sea (and, in the WW1 era, in general) might only penetrate seawater for a few meters in real-world That meant that submarines had to surface in order to communicate, another de facto limitation on their endurance while submerged.

The Navy had been evaluating electronic communication aboard ships since 1887, when they demonstrated a simple and "radio-adjacent" technology using conduction of waves through the seawater itself. This scheme never worked very well, but was saved by the development of modern wireless transmitters late in that century. Marconi himself demonstrated radio to the Navy in 1899, and in 1903 the Navy bought its first radio sets. Tactical reports from conflicts elsewhere on the globe, like the Russo-Japanese war, reinforced the idea that radio would serve a key role in naval combat.

When C-class submarines Stingray and Tarpon, and D-class Narwhal, launched in 1909, they were immediately given duties including the evaluation of radio equipment. In a classic tale of early technology, the evaluations went poorly. Tarpon ran into mechanical trouble that prevented its planned trial voyage, so the radio set was never installed. Stingray received a cutting-edge quenched spark gap transmitter and receiver set, but the transmitter turned out to be DOA. Still, Stingray was able to demonstrate its receivers, copying a message from the nearby Boston Navy Yard while surfaced.

Narwhal's mission was more ambitious: underwater communication. A test was made on the same direct conduction technology, using brass plates suspended below the ships, demonstrated in 1887. It similarly failed to perform. A repetition of those experiments, done the next year and with improved equipment aboard Narwhal's sister ship Grayling, produced better results. The system provided reliable communications with the "antenna" plates submerged as much as two feet below the water... and no deeper. Frustrated Navy engineers concluded that it was possible to get radio signals through seawater, but not practical.

Through the First World War and following decades, engineers focused on ways to get the antenna to the surface without having to bring up the entire submarine. Around 1915, the Navy adopted a floating antenna buoy that a submarine could "winch up" towards the surface on a cable. Putting anything at the surface was less than ideal, but the anti-submarine technology of the era the small antenna buoy was still very difficult to detect at long range. Submarines just had to make sure it was retracted back to the submarine's deck before attempting anything where stealth was key. These floating buoys were not reliable during WW1, but they could work, and the technology has continued to develop to this day.

Still, there were other ideas about underwater communications. The most important development came from two engineers of the National Bureau of Standards (NBS), or at least, that's what a court ruled after a patent dispute between two sets of supposed inventors. John Willoughby was employed by the NBS, which would later be known as the National Institute of Standards and Technology (NIST), to investigate new types of radio receivers. In the summer of 1917, he was arranging various types of coil antennas at a receiver test site on the Chesapeake Bay when he accidentally dropped one of the antennas into the water. Strangely enough, the radio receiver connected to the antenna continued to provide good reception even as it sank into the bay.

NBS management was not especially enthusiastic about this accident, but Willoughby was. He knew that the Navy was investigating means of communication with submarines, and that seawater seemed to block radio waves, all of which suggested that he might have stumbled on an important discovery. Lacking NBS support for further research, he took the idea to gifted radio inventor and NBS colleague Percival Lowell 1. In a fine tradition of innovation, the two took to Willoughby's basement for a series of experiments that illuminated the underlying phenomenon: Willoughby had been experimenting with unusually low radio frequencies, below 30kHz where wavelengths become too long for most antenna designs and coils become the best receivers. These lower frequencies were significantly less affected by water than higher, more conventional frequencies, and Willoughby and Lowell built a successful prototype for what they called "long-wave" radio between two coils.

The NBS remained surprisingly uninterested, but Willoughby had a contact in the Navy who felt quite differently. In 1918, Willoughby and Percival joined LtCmd H. P. LeClair, then running the Navy's experimental radio program, at submarine base New London (so named after New London, Connecticut, across the Thames River (Connecticut) from the base). They made a hurried and rough installation of their equipment on submarine D-1 and a surface support vessel. Not everything went perfectly, but they proved the idea: Willoughby, Lowell, and LeClair listened attentively to their radio sets as the D-1 submerged and continued to come in loud and clear.

Within a matter of a few years, the Navy accepted long-wave radio as a standard technology for submarine communications. The various jury-rigged installations at New London showed that coil antennas could easily be integrated into a submarine's rigging, and even better, the Navy had found that long-wave radio propagated over the surface as well as under it. Long-wave communications would serve the entire Navy, and a transmitter site was already underway.

Long-range communications had become a top concern throughout the military in the early 20th century, and a series of meetings between US military branches and between the US and UK lead to a scheme of "High Power" radio stations. The first of these, NAA, went up near Arlington, Virginia in 1913. Over the following years, similar stations were built in the US and Europe, facilitating the first direct communications between the two and the first transatlantic voice communication in 1915. The construction and operation of these stations also lead to considerable advances in radio technology generally, especially powerful transmitters. NAA was one of the early stations to be equipped with Poulson arc transmitters, almost two times more efficient than earlier designs and well-suited to long-wave operation.

Around the same time as the Willoughby/Lowell experiments, Navy engineer LtCdr Albert Taylor found similar results with long-wire antennas shallowly under the water. These experiments offered another design for concealed submarine antennas (which could be stored onboard in reels and let out with floats that kept them just under the surface), and also demonstrated that long-wire antennas could be buried for transmit use.

Five years later, in 1918, construction was underway on NSS—a new high power station in Annapolis, Maryland. Unlike those before, NSS was specifically designed for long-wave signals. Two 500 kW Poulson arc transmitters driving an antenna 400' square and suspended between four 500' tall towers 2. The long-wave capability at Annapolis was not originally intended for submarine communications, but it quickly fell into that niche. During the 1920s, NSS became a key station for submarine command and control of submarines.

NSS itself remained in service until 1996, and it was joined by VLF transmitters at Cutler, Maine; Jim Creek, Washington; Lualualei, Hawaii; LaMoure, North Dakota; and Aguada, Puerto Rico; besides sites in Europe operated with allied militaries. Each of these stations is its own interesting story. The 1,205' VLF antenna tower at Aguada remains the tallest structure in the Caribbean. LaMoure was originally built in the 1960s for a long-wave navigation system called Omega, and was repurposed for submarine C2. Jim Creek went into service in 1952 as the most powerful radio transmitter in the world, using a fascinating antenna that draped from one ridge to another across a mountain valley.

Let's focus, though, on Cutler. VLF Transmitter Cutler is the spiritual descendant of the Navy's original High Power program, symbolized in its inheritance of the callsign NAA. Cutler was part of a Cold War expansion of the VLF system, going into service in 1961. Many other VLF sites received upgrades around the same period, but Cutler was a completely new design. Cutler's two antennas, for redundancy, are each supported by 13 towers. The center tower is about 1,000' tall, and the other 12 make up two concentric rings of about 900' height. The complete antenna is over 6,000' across, or nearly 2 km. Between the tower tops stretches a web of tight horizontal wires, each 1" copper, that form an enormous capacitor. The capacitor's other plate is the ground, electrically reinforced by many miles of buried groundplane wires. The radiating elements are vertical wires, hanging down from the upper horizontal mesh.

In Maine's harsh winters, the wires accumulate ice until their weight threatens the towers. Each antenna is alternately switched into a deicing mode in which it is turned into a 3 MW heating element... just for long enough that the ice melts off. Outer towers are supplemented by short, stout structures that allow the 220 ton tension weights to move up and down on tracks. "Helix houses" at the feedlines of the two antennas sheltered enormous inductors; walls lined with copper served as insulation and to ground the occasional arcs that made the helix houses and transmitter rooms unsafe to enter during operation.

The two antennas were driven by a transmitter complex designed and built by Continental Electronics. The 11 MW on-site power plant supplied the AN/FRT-31 transmitter, custom to this installation, consisting of four parallel units of eight ML-6697 transmitter tubes. The transmitter's control room rivaled that of many power plants, as did its output: the military required at least 1 MW, Continental rated the transmitter for just over 2 MW, and it still operates today at powers as high as 1.8 MW. There are several reasons that the "most powerful radio station in the world" is now difficult to pin down, but NAA Cutler is certainly in the running.

That is the end of the VLF story, in that it hasn't ended. The original 1910s and 1920s VLF sites are mostly decommissioned, but only because they have been replaced by more modern equipment, sometimes on the same site. Cutler, Jim Creek, Lualualei, and Aguada are all still in service. LaMoure may be in some kind of mothballs state but is definitely capable of operating, it has recently seen some use for propagation experiments. VLF is still a key technology in the Navy's C2 and nuclear reprisal plans. So, we can say that VLF has achieved one of the great feats of technical history: it has outlived its replacement.

First, though, we should spend some more time on the theory. In modern parlance, "VLF" describes the band from 3-30 kHz. Most Naval VLF stations operate at around 24 kHz, but some stations support lower frequencies as well and other stations have operated as high as 40 kHz (still considered VLF by the Navy for practical purposes). These wavelengths pass through seawater well because of a basic trait of radio waves that was becoming experimentally apparent in the 1920s and received a thorough theoretical underpinning later. Radio waves attenuate as they pass through materials in proportion to the number of wavelengths in the material. In other words, as a rule of thumb, a radio wave with a 12 m wavelength (~24 MHz) will experience about 1,000 times the attenuation of a signal with a 12,000 m wavelength (~24 kHz). This is true of water or air or any other material, but the attenuation rate in saltwater is so high that the effect is extremely apparent in the sea.

This brings us to our first property of VLF: because of the long wavelength of VLF signals, they pass through water with relatively little attenuation. Still, there is a limit. The details of submarine communications are mostly classified, but from open materials it is realistic for a submarine to receive a VLF transmission up to about 100' below the surface. This depth is already far better than what's achievable with HF, and far superior to deploying a floating buoy. Still, intuition dictates that even lower frequencies could be even better, and the Navy did not go without noticing that possibility.

Second, we should revisit the antennas. One of the key insights of early experimenters like Willoughby and Lowell is that coil antennas create an asymmetry in radio communications. Antennas become more efficient as they reach the wavelength of the signal, or multiples thereof. That means that lower frequencies, and longer wavelengths, require larger antennas—thus the 6,000' wide cobwebs at Cutler and more than one regional height record set by VLF antenna towers. On the other hand, coil antennas, or more specifically magnetic loop antennas, can be very small compared to the wavelength they receive.

Unfortunately, the physics trick that makes magnetic loop antennas work so well (magnetic coupling) is basically one-way. Magnetic loop antennas are relatively inefficient but usable for reception; they're completely useless for transmitting. VLF is effectively a one-way technology, and some of the traffic carried by the Navy's VLF network consists simply of orders for submarines to surface or deploy a buoy for more advanced communications.

Finally, we should observe that the capacity of a radio channel to carry information is proportional to its bandwidth, and that the use of lower frequencies and longer wavelengths makes the usable bandwidth of given radio equipment much smaller (we can intuitively understand this by noting that larger antennas are, simply due to scaling, more precisely tuned to their intended wavelength than smaller antennas). VLF transmitters are only capable of very narrow transmissions, functionally limiting them to continuous wave (Morse code) operation or simple digital schemes at very low speeds.

We probably all realize, as did the Navy, that pushing to yet lower frequencies and longer wavelengths would produce better penetration of the seawater, at the cost of basically every other property becoming worse: larger antennas, less efficient transmitters and receivers, narrower bandwidths. The possibility of going even further—from Very Low Frequency to Extremely* Low Frequency—was just a solution in wait of a problem. The military had a lot of those, and the Cold War was one huge problem.

The idea of a nuclear-powered submarine is almost as old as the nuclear program, and a collaboration between the Navy, the Atomic Energy Commission, and famed admiral Hyman Rickover lead to the 1951 launch of nuclear-powered submarine Nautilus. The next decade gave the Electric Boat Company new meaning, as nuclear propulsion displaced diesel in the US submarine fleet and fundamentally changed the strategy of submarine warfare. Nuclear submarines, unlike those using diesel-electric or gasoline propulsion, can be set up to remain submerged almost indefinitely. The reactor does not require air, and provides plentiful power for life support equipment that mitigates the fresh air requirement for everything else. This created a generational change: by some definitions, all pre-nuclear submarines were merely submersibles, ships designed to submerge only temporarily. The nuclear submarine was a new kind of creature, one that not only visited the depths but could live there.

Add in the development of submarine-launched ballistic missiles (SLBMs), which enabled a submarine to direct nuclear weapons at targets on shore with shorter travel time than any other means of delivery. Every submarine became a portable missile silo, one that could not only hide but actively evade detection. Their ideal mission was to lurk, undetected, for extended periods of time.

Of course, this new potential for submarines further stressed communications infrastructure. A nuclear submarine might spend weeks submerged in water that is ostensibly controlled by another nation, making stealth critical. Such a submarine doesn't want to remain close to the surface, which makes detection by all means easier, and also doesn't want to deploy floating buoys or antennas that are easily detected by modern radar. On the other hand, for it to have any value as a nuclear deterrent, the Navy needs some way to deliver a launch order without having to wait for the next duty rotation.

The military spent the early Cold War developing a dozen different systems for survivable delivery of nuclear war orders, things like the High Frequency Global Communications System (HFGCS) and TACAMO that solidified the concept of short, simple, one-way Emergency Action Messages to direct nuclear forces. The Navy needed a way to deliver EAMs to submerged submarines, and that provided the impetus to investigate lower frequencies than ever before.

The lowest generally recognized radio band, ITU band 1, is Extremely Low Frequency or ELF. There is some historic complexity around the definition of ELF, and the modern range of 3-30 Hz does not exactly match the way the Navy has used the term. In general, though, we can consider ELF to refer to the very bottom end of the usable radio spectrum. The extreme lower edge could be said to fall around 7 Hz, where the wavelength of a radio signal matches the circumference of the earth. This leads not only to complex interference problems due to constructive and destructive interactions, it also produces a very high noise floor as global lightning storms trigger perturbances that resonate on and on. Balancing the desire for the lowest possible frequency against the practical challenges of ELF, the Navy settled on the range of 72-80 Hz as the most promising window for submerged submarines.

The history of Naval ELF development is not simple to research. First, the Navy conducted much of its ELF research in secrecy, a result of typical Cold War paranoia and an awareness that the Soviet Union was pursuing a similar idea. Second, much like GWEN, ELF became the locus of fervent public opposition grounded in general anti-war sentiment, demands for nuclear disarmament, and the safety of electromagnetic radiation. Many of the readily available sources on ELF history today come from "electrosensitive" advocates or newsletters, a still-strong movement founded on the mostly unscientific premise that EM fields pose a danger to human health. While mostly factually accurate, these sources require some caution since they tend to mix their historical narrative with observations about EM and RF safety that are now broadly considered pseudoscientific. Still, this frustration leads to two positive outcomes: first, it helps to place the development of ELF radio within a broader cultural context of uncertainty about both war and new technology, emphasizes the unknowns involved in the push to ELF, and makes the ELF stations an interesting focus of the anti-war movement. Second, it leads to a personal connection that likely contributed a great deal to my interest in military communications.

There are rumors, even scant evidence, that the Navy initiated classified experiments with ELF in the late 1950s. There is very little that I can say about this first part of ELF history, besides that the experiments must have had promising results. In 1968, the Navy adopted a full-scale ELF communications plan called Project Sanguine.

The original Sanguine proposal was truly an artifact of the Cold War, remarkable in its scale and doomed to obsolescence before construction even began. The Sanguine ELF station would actually be over one hundred independent transmitting stations, operating in synchronization as a form of hardening. The loss of a subset of those stations, say due to nuclear attack, would only reduce power rather than disabling the entire facility. Of course, to maximize survivability of the individual transmitters, they would all be installed in hardened underground bunkers, each with a set of 2" antenna cables extending 40 or more miles in four directions. The overall layout of stations and antennas created a grid with antenna elements spaced every 3-5 miles, covering a total of some 6,500 square miles. That's larger than Connecticut, but smaller than New Jersey. Perhaps more apropos, it is about 1/10 the area of Wisconsin, the state where the Navy planned to install the system 3.

This underscores a fundamental problem with ELF: antenna sizes. At 80 Hz, the wavelength of a radio wave is 2,300 miles, or about one quarter of the diameter of the earth. Take, for example, a half-wave dipole antenna—a very common antenna design in most bands. For ELF, the antenna would need to stretch from Albuquerque to Portland. Clearly, then, any practical ELF antenna needs to be "electrically short" or, in the relative sense of RF engineering, a small antenna. Small antennas are inefficient, and the smaller they get the less efficient they are. Complicating things further, practical ELF propagation over the surface of the earth requires vertically polarized waves. That means a vertically polarized antenna, and there is simply no way to construct a tower that is hundreds of miles tall.

Sanguine proposed, and most later ELF projects adopted, a style of antenna called a ground dipole. A ground dipole is basically two different electrodes, or grounding rods, driven into the ground a great distance apart and connected by feedlines. The power from the transmitter goes through the electrodes into the ground, where it flows as ground current from one end of the antenna to the other. The ground dipole thus forms a loop, with the feedlines as one side and the ground as the other. The actual RF emission results from the magnetic field between the feedlines above ground and the current flowing beneath, somewhat like the VLF antenna at Annapolis if half of it was buried beneath the ground.

Ground dipoles, like a typical dipole antenna, are directional. They emit RF most strongly in the same axis as the antenna, with strong lobes extending away from the ends of the two feedlines. By installing a second antenna on a perpendicular axis and shifting the phase between the two, you can create a steerable antenna with its strongest lobes pointed in the direction of your choice. That's why the Sanguine proposal, and most ELF transmitters after, have used two ground dipoles in a crosswise layout.

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During the 1960s, the Navy performed a series of poorly documented experiments to establish the feasibility of Sanguine. These included a Wyoming power transmission line that was temporarily disconnected for use as an ad-hoc 40 mile antenna, and a power-line-like 110 mile antenna built by RCA in North Carolina and Virginia. The details of this RCA experiment, part of Project Pangloss, have become obscure. It appears that RCA was contracted to evaluate a number of different communications options for the Navy, including the use of other planets in the solar system as passive repeaters, but most of them didn't work out. The VLF transmitter for the project was located at Ararat, North Carolina, and the two two electrodes at Algoma, Virginia and Lake Lookout, North Carolina. A 1963 test successfully got a message from the test antenna to a submarine submerged 150' deep and 520 miles from the transmitter.

Like most of the military's ambitious plans in the late 1960s, Project Sanguine didn't happen. The reasons are complex, or at least several. Sanguine was unpopular with the public: besides specific concerns around safety, the late '60s saw a rising anti-nuclear campaign and a general lack of interest in enormously expensive military undertakings. The fact that Sanguine needed a massive amount of land meant that it was pretty much impossible to site it somewhere that wouldn't generate local opposition, so like ICBM fields, Sanguine was kicked around like a football. Originally planned for Wisconsin, it later shifted to Texas, and Texas didn't like it that much either (although by that point the antenna field had been downsized to just 1,600 to 3,200 square miles). And, of course, the technology was struggling to keep up with the threat landscape. The hardened design of Sanguine relied mostly on the idea that the Soviet Union couldn't possibly nuke most of the transmitters distributed over 6,500 square miles, a reassurance that the development of multiple independent reentry vehicles (MIRVs) seriously undermined.

As public opposition formed, a health and safety review commissioned by the Navy resulted in a noncommittal report that did little to reassure the public (and lawmakers) that the plan was safe. Last of all, but certainly not least, the budget projections for Sanguine were formidable, and Congress did not have the appetite for the spending.

Sanguine made it far enough that, during 1968, the Navy and RCA built a scaled down transmitter and antenna in the Chequamegon National Forest of Wisconsin. This came to be known as the Wisconsin Test Facility, and it was used as a transmitter for a series of jamming tests in the late '60s and early '70s. During this period, the Navy also considered the use of a BPA transmission line from The Dalles, Oregon to Los Angeles as an ELF transmitter—the plan being to actually modulate messages onto the 60 Hz AC power carried by the line, which was incidentally radiated due to the line's largely straight 850 mile span. This plan was called PISCES, and it is unclear if it ever went anywhere, although an interesting rumor holds that it was operational for a short period and used as the "jammer" transmitter for jamming susceptibility testing of the Wisconsin transmitter.

The results of these tests were mostly positive, but that wasn't enough to save an unpopular plan. Sanguine faded away, perhaps replaced by a scaled-down system called Super Hard ELF or SHELF. There is very little information on SHELF today. The idea seems to have been to install an ELF antenna in deep underground shafts (potentially over a mile below the surface) using hard-rock mining techniques. Work on SHELF apparently continued through the 1970s, but it probably never got beyond the feasibility stage.

Instead, the Navy shifted its focus to Project Seafarer. Seafarer was clearly a direct descendant of Sanguine, but addressed many of its biggest problems through a stripped down design. Seafarer transmitters, for example, would be located in surface buildings instead of underground. Still, the same basic antenna design remained, a grid on 3.5 mile spacing requiring about 4,700 square miles. The Nevada Test Site was considered as a location, as was White Sands Missile Range and forestland in the Upper Peninsula of Michigan. Michigan was ultimately selected, a result of favorable ground conditions and the lack of frequent large explosions. Seafarer construction was expected to begin in 1977, but instead it ended. The governor of Michigan shot the idea down, Congress didn't like it all that much, and President Carter signed the order ending work on not only Seafarer but ELF in general. In 1977, after roughly two decades of R&D work across multiple experimental sites, the ELF Program was in mothballs.

The Navy was not so easily dissuaded. Later in 1977, they proposed "Austere ELF," a plan to throw together an ELF transmit site more or less from spare parts. A transmitter at Sawyer AFB in Michigan's Upper Peninsula would feed 32, 45, and 53-mile-long antenna elements, and via a leased telephone line the AFB would also control the inactive Wisconsin Test Facility transmitter. Even this basic, partially spare parts plan fell afoul of the public and congress. It failed to address most of the original health and environmental concerns, and still cost too much.

Serious resumption of the ELF program would have to wait for President Ronald Reagan. Reagan was a fan of big, expensive, technically sophisticated solutions to Cold War programs, and ELF sure was one of those. Reagan approved "Project ELF," itself a scaled down version of Austere ELF. Project ELF used the existing Wisconsin Test Facility, supplemented by an identical 56-mile antenna in Michigan's Escanaba State Forest. Both would be operated by Sawyer AFB.

The Wisconsin Test Facility from Project Sanguine, after 20 years, came to be known as Navy Radio Transmitter Clam Lake: the first operational ELF transmitter. The Michigan site, known as Navy Radio Transmitter Republic, quickly joined it.

It's amusing that a temporary test facility ultimately became the final product, but the Navy had already invested a huge amount of effort in the Wisconsin transmitter. Everything from the strength of the EM field produced by the transmitter to its location in a National Forest had posed complications.

Although Sanguine was intended as a hardened, underground system, burying antennas was a lot of work and the Wisconsin Test Facility had originally been temporary. Instead of buried cables, it used 1/2" aluminum wires strung above ground on utility poles for the two antennas. The voltages on the antenna wires required isolation from the surrounding environment, so as with power lines, trees were cleared to make a right of way for the antenna cables. The Forest Service, concerned about aesthetic impact on the forest's recreational areas, required that the antenna routes avoid some parts of the forest and take right-angle jogs near roads so that it was not possible to see a considerable distance down the antenna ROW when driving past (which would make the existence of the cleared ROW much more obvious). The transmitter site and antenna ROWs are still clearly visible today. At each of the four ends, about seven miles from the transmitter building, around 10,000 feet of buried copper wire make up the electrode.

Trickier were the electrical problems. The ELF antennas could induce a significant potential in parallel electrical lines, and the use of ground return meant a lot of interference on telephone lines. When transmitting, which was ultimately the case 24/7, the 2.6 MW transmitter induced a current of about 300 A in the cables and ground. Understanding these impacts of ELF transmitters was actually one of the original purposes of the Wisconsin Test Facility, and the Navy had built model power and telephone lines parallel to the antenna elements. The ELF system was found to cause problems ranging from flickering light bulbs to phantom telephone ringing, and the Navy installed additional grounding and filtering on public utilities throughout the area at its own expense—even reimbursing the utilities for administrative costs related to customer complaints. Still, the interference problems were not fully solved during the test operations and no doubt contributed to the public's less than enthusiastic support.

The former Wisconsin Test Facility, as Clam Lake, became operational in 1985. Its sister site, Republic in Michigan, went online in 1980. Republic was new construction, not an old experimental facility, but for cost and expediency reasons it was a virtually identical design to Clam Lake with above ground wires to buried electrode screens. Because of geographical constraints, the Republic antenna is not in a straightforward cross configuration. Instead, it's more of an "F" shape, electrically equivalent but with the feedlines placed differently. From 1989 on, the two sites operated in synchronization, with their total 2.6 MW operational transmitter power producing a radiated power of about eight watts.

Yes, even at 14 miles in length, ELF ground dipoles are extremely inefficient. This remained a key problem with ELF. Early Navy ELF plans, like Project Sanguine, had assumed the use of extremely high transmit powers to produce a usable signal. ELF propagates very well, but at the paltry 8 W achieved by the Project ELF transmitters, practical reception still required extracting the transmitted signal from a noise floor that was just about as loud. That meant reducing the practical bandwidth of the system even further, and thus its speed. Project Sanguine would probably have been able to transmit EAMs directly to submarines; Project ELF was not. Even the compact format of EAMs was too long for a system with an effective symbol rate of about one letter per five minutes, or fifteen minutes to transmit the three-letter code groups used by the Navy.

This reduced ELF capability was basically a very fancy pager network. The Navy has not disclosed the details of the scheme, but it's probably something like this: each submarine has a three-letter code group assigned to it. When its ELF receiver detects that specific code group, the submarine crew know that there is a message waiting for them, and they have to move at least close enough to the surface for VLF in order to find out what that message is. The Navy often referred to this as "bell ringing:" ELF messages were like the ringing of a telephone. As a means of supervision, so that submarines knew they were capable of receiving a message, "idle" code groups were transmitted 24/7.

For how hard the Navy had fought to build it, Project ELF did not have a long life. The Navy's ELF submarine communications system was conceived around 1958, became operational over 30 years later in 1989, and shut down in 2004 after just 15 years of service. "The Nuclear Register," an anti-nuclear-weapons newsletter, put it like this: "A surprise Navy announcement signaled the end of 36 years of first local, then global, opposition to the Navy's giant transmitter system."

ELF overcame formidable political odds. Besides Congress's lack of interest in the expense and federal policy concerns around health and the environment, a statewide ballot referendum in Michigan had attempted to prohibit construction and legislation prohibiting ELF transmitters was perennially introduced in the federal congress. Activist groups opposed to the transmitters staged regular demonstrations and, as Project ELF proceeded despite their objections, protests gave way to civil disobedience. Utility poles supporting the ELF cables were cut on numerous occasions, and the transmitter buildings vandalized. "The Nuclear Register" wrote:

Nukewatch said the Navy's closure announcement, while welcome, raises more questions than it answers. The Navy said "improved technologies" and "changing requirements of today's Navy" made ELF obsolete. However, "very-low-frequency (ELF) [sic] alternatives to ELF have been around for 30 years and the 'changing requirements' refer to the end of the cold war that happened 14 years ago," LaForge said.

Indeed, it is hard for me to see the undignified closure of the Navy's ELF program as anything other than an admission of failure. The basic technical concept of ELF appears sound, but the transmitters are large, disruptive, and costly to operate. It is not clear that the advantages of ELF, namely the greater depth at which it can be received, outweigh its downsides or compare well to VLF.

VLF is still used by the US Navy today. ELF is not: the US has had no ELF capability since the 2004 closure of Clam Lake and Republic. China, India, and Russia are the only other nations to have constructed ELF transmitters. The Russian system, ZEVS, operates at 82 Hz from ground dipole antenna in place since at least the early 1990s. It is a candidate for the most powerful radio transmitter in the world, although the exact specifications have not been made public. India's INS Kattabomman gained an ELF transmitter in the 2010s, and while few details are known, China is believed to have constructed an enormous ELF transmitter in Huazhong during the 2010s.

It is, of course, interesting that China and India have both built an ELF capability after the US abandoned the technology. One wonders what made an ELF capability so hard to sustain here, even after the Clam Lake and Republic sites were built. Well, there is an inertia to politics: the organized opposition to ELF, once energized, didn't go away. Area residents and politicians continued to organize for the closure of the Wisconsin and Michigan transmitters until their final days.

Opponents of the ELF sites got plenty of help from both science and popular culture. Preliminary research linking ELF radiation to leukemia has not held up to modern scrutiny, but as with broader EM/RF cancer links this is an area of ongoing controversy. Extensive research by the Navy, mostly on the Clam Lake Site, hasn't found evidence of ecological disruption due to the ELF transmitter. Still, there is ongoing controversy, and one of the reasons for Project ELF's long and torturous construction process was a series of lawsuits and appeals under the National Environmental Policy Act, contesting the thoroughness of the environmental research.

As usual, these possible connections to health and environmental impacts have given way to conspiracy theories. In the more shadowy corners of the internet, ELF is associated with everything from strange sensations to mind control. And that is where I first became involved.

The X-Files episode "Drive" (S06E02) sees Fox Mulder cornered, practically carjacked, by a man who insists that if he does not drive West then his head will explode. The episode aired four years after the release of Speed and no doubt owes inspiration to that film (Mulder even makes a joke about it in the episode), but it attributes the bizarre scenario to a very different cause. The hapless victim, portrayed by Bryan Cranston, gained his head-exploding illness as a result of some sort of military experiment involving long antennas secretly buried beneath his house. Vince Gilligan wrote the episode, and while there were several influences, the final episode is a direct reference to Project ELF and the surrounding controversy. Years later, because of their collaboration on "Drive," Vince Gilligan cast Cranston as the lead in his show Breaking Bad.

In the episode, Cranston doesn't make it to the West Coast. Mulder and Scully hatch a plan to puncture his inner ear and relieve the pressure building in his brain somewhere on the California coast, but Mulder just can't drive fast enough. Cranston's head explodes.

Over the lifespan of the Project ELF facilities, police issued 636 trespass citations to demonstrators. Congressional representatives introduced legislation and amendments to end the ELF program multiple times. At least a half dozen ELF transmitter concepts were canceled, each one less ambitious than the ones before it. ELF is an interesting technology, but in a way, it's more interesting as a case study in military acquisition.

Take a concept that is expensive, politically unpopular, and questionably superior to systems already in service—but if the military wants it, they tend to eventually get it. After thirty years, the military wears resistance down and gets something pushed through. Fifteen years later, the Navy shrugs, calls it obsolete, and shuts it down. What's left is a 14-mile-across "X" in the forests of Wisconsin, a legacy of controversy that still echoes, and a pretty good episode of The X-Files.

1. Unrelated to astronomer Percival Lowell, although there are enough moments of intersection between the two that you wonder if they might have met.↩

2. Many of the fine details of the original NSS installation have become confused, probably because the Navy upgraded the equipment several times in its first decades and the specifications of different eras have become confused. Here are some notes: some sources give the transmitters as 350 kW, others as 500 kW. A Navy history explains that improvements to the antenna design allowed for raising the power after the site was originally designed, so 500 kW is indeed what was installed but we know where the 350 number came from. Some sources give the original towers as 500' tall and others (including Wikipedia) 600', I think the 500' number is more reliable as it agrees with the Navy history. I am not quite sure where the confusion comes from, though.↩

3. Some sources, such as Wikipedia, give a number of 22,500 square miles and 2/5 the area of Wisconsin. This was the very top end of a preliminary estimate that was revised down to 6,500 during planning. The 22,500 number still frequently appears, probably just because it's the more absurd figure, which is an example of the challenges of historical research when most information comes from activist groups opposed to the thing you're researching. Of course, we have to temper that criticism with the fact that some anti-Sanguine sources use the 6,500 figure, especially older ones. The shift towards the more attention-grabbing 22,500 might have happened later as Sanguine was discussed more by people without original knowledge of the program.↩