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 . 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 . 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 .

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.

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.