http://www.fas.org/nuke/guide/usa/c3i/f ... lf2003.pdfhttp://www.fas.org/nuke/guide/usa/c3i/elf.htmExtremely Low Frequency Communications Program
How ELF Communications works
ELF communications systems make use of a principle in
physics where the attenuation of radio signals
(electromagnetic waves) from seawater increases with
the frequency of the signal. This means that the lower the
frequency a radio transmission, the deeper into the ocean
a useable signal will travel. Radio waves in the Very Low
Frequency (VLF) band at frequencies of about 20,000
Hertz (Hz) penetrate seawater to depths of only tens of
feet.
 The Navy’s ELF system operates at about 76 Hz,
approximately two orders of magnitude lower than VLF.
The result is that ELF waves penetrate seawater to
depths of hundreds of feet, permitting communications
with submarines while maintaining stealth.
In conjunction with the development and construction of the ELF system, the Navy sponsored a variety of
environmental and ecological studies. In the 1970's the Navy sponsored a wide range studies, most being laboratory
studies, that were conducted by independent researchers and Navy laboratories. This research culminated in a 1977
review by the National Research Council (NRC) of the biologic effects of electric and magnetic fields associated with
the proposed Seafarer system. The NRC concluded, “… the likelihood of serious adverse biologic effects of Seafarer
is very small.” In conjunction with the upgrade of the ELF system in the mid-1980's, the Navy initiated two additional
efforts; a literature review and an unprecedented ecological monitoring program. The American Institute of Biological
Sciences (AIBS) was requested to provide an evaluation and analysis of the extant professional literature published
since January 1977 about biological and human health effects of extremely low frequency non-ionizing
electromagnetic radiation germane to the Navy's ELF system. In 1985, the AIBS concluded in its report, "
It is unlikely
that exposure of living systems to ELF electric and magnetic fields in the range of those associated with the Navy's
ELF Communications System can lead to adverse effects on plants and animals." The unprecedented twelve year
ecological monitoring program, which began in 1982, included in situ studies near the transmitter facilities in both
Wisconsin and Michigan. At the conclusion of the field studies, the Navy requested the National Research Council to
review the findings of the twelve year program. In 1997, the NRC committee published its findings which agreed with
The ELF frequency range is critically important to the Navy because of its value in providing a way to communicate with submerged submarines. As a result of the high electrical conductivity of sea water, signals are attenuated rapidly as they propagate downward through it. In effect, the sea water "hides" the submarine from detection while simultaneously preventing it from communicating with the outside world through normal radio transmissions.
The degree to which a signal is attenuated depends on its frequency, however. The lower the frequency, the more deeply a signal can be received in sea water. In order to receive conventional radio transmissions a submarine must travel at slow speeds and be near the surface of the water. Both of these situations make a submarine more susceptible to enemy detection. Frequencies in the ELF range, however, can be received considerably deeper, and broadcasts using this mode provide a primary link between the nation's commander-in-chief and the submarine force. 
The US Navy extremely low frequency [40-80Hz] experiment Project Sanguine installed a 222km pole mounted dipole antenna high up in the Laurentian Shield in Wisconsin - upgraded to the 45km Project Seafarer antenna at Clam Lake, Wisconsin. Following an unsucessful standoff between environmental lobbyists and Ronald Reagan in 1981 a futher Seafarer upgrade featuring 90km wires was installed KI Sawyer Air Force Base, Michigan, incorporating operational VLF into the integrated C3i program of the American Department of Defense. VLF links between the Wisconsin station & submarine receivers in the Pacific were established in May 1985, followed by transmissions to beneath the Mediterranean Sea and Northern Polar Ice Cap.
Geological Requirements
An ELF antenna sends a signal from the ground to the ionosphere where it travels around the world filtering down through the ocean depths to reach the fleet of submarines (see figure above).  Due to the limits of the lengths of the system’s antennas (less than 100 miles versus the required 2,500 miles to generate a 76 Hz electromagnetic wave), 
the antennas are placed near nonconductive rocks from the Precambrian era.  To be useful, the rock formation must be fairly close to the surface and be large enough to support the ELF antenna grid.  The rocks must be as nonconductive as possible so as not to “shorten” the electromagnetic wave.…and a German    
ELF was accidentally detected in World War I when the Germans noticed a very low frequency noise in the ground which had a strong resonance at 7 Hz  [The] Germans felt that the noise was caused by electrical storms.  The phenomenon was dismissed as interesting but of no practical use.  It was not until the early 1950s that interest in ELF began again.  In 1952 a German scientist named W. O. Schuman pointed out the existence of a cavity between the earth and the ionosphere  that has a fundamental resonant frequency of about 7 Hz.  A radio wave having the same frequency [NB: one more time, it isn’t a “radio” field!] can be broadcast into this cavity [and] will travel 25,000 miles around the world at the speed of light.  [Other] scientists quickly added to Schuman’s discoveries.  They found out more about the resonances: frequencies below 100 Hz do not fade out.  [These] discoveries set the stage for the ELF concept.     
L. W. Klessig and V. L. Strite (The ELF Odyssey)
	Few places in the United States meet those conditions, Wisconsin and Michigan being the best two.
FIRST MADE PUBLIC by the US Navy in 1968 as Project Sanguine (1), the Extremely Low Frequency communications project—Project ELF—is designed to communicate with deeply-submerged submarines.  
Project ELF uses low-frequency waves to signal one-way coded messages to US and British Trident and Fast Attack submarines. The system alerts them to surface to receive a more detailed communication. 	
ELFS IN THE FOREST         
Each facility consists of a transmitter, pole-mounted antenna cables, and buried ground terminals where the antenna currents enter the earth.  The Navy Radio Transmitting Facility (NRTF) transmitters are located near the intersection of the antennas in each site.  The NRTF at Clam Lake has two orthogonal antennas, one essentially oriented north-south (NS) and ther other east-west (EW), resembling a large “X.”  Each antenna is 14 miles long and carry 300 amperes.  The NRTF at Republic has one NS antenna (28 miles) and two parallel EW antennas (14 miles each), the whole system resembling an enormous “F”; overall current is 150 amperes.  The transmitters have been operated either synchronously or independently to broadcast messages.