Electromagnetic Waves

An ELF

Submarine ELF communications are one-way, to the sub. The baud rate is very low and so short codes are used. They're repeated to make sure they're understood correctly. Moreover, the codes are carefully designed to minimise the chance of being accidentally interpreted as being some other, legitimate code. These codes are so-called one-time pads, a simple but very effective encryption technique as old as the hills.

One-time pads cannot be decrypted because they themselves contain no information apart from the other half of the OTP, the code-book. The code-book associates the codes with their meanings. The assignment is arbitrary but once agreed-upon, it is fixed. Either one without the other is completely useless. I used OTPs to send messages in class to my friends in primary school. It was fun and even when we were caught (and we were) the teacher couldn't tell from the codes what we were 'saying'. The obvious disadvantage is the fact that the contents of the code book must be agreed-upon a priori, which means the parties must communicate the contents by other secure means - usually in-person.

An example of a sub's use of ELF-transmitted OTPs might be:

r3J - Go to periscope depth, deploy TDRS satellite antenna buoy and wait for instructions via Channel 3417 encrypted via Key #5587

wLt - Set course for Bravo Charile. (whatever that means to the sub commander)

etc - et cetera

Low-frequency radio waves are used for sub communications because low frequencies are the only ones which can penetrate highly-conductive sea water to any depth. The U.S. Navy uses extremely low frequency radio waves for this reason. They used to operate ELF stations in Michigan and Wisconsin, USA, but these have long since been decommissioned in favour of other approaches. I believe the carrier frequency the old installation was 76 Hz.

Because ELF radio waves have such very long wavelengths, they require huge aerials in order to transmit efficiently. Impractically huge if any efficiency at all is to be gained. The ELF system the Navy used in Michigan/Wisconsin pumped over a megawatt into the 'aerial' which itself was comprised of an underground current path back to the transmitter. A dirt & rock aerial effectively! The site was chosen for its soil conductivity, mainly. The wires you see stringing from pole-to-pole in old photos of the system were simply the feed-lines for the aerial, not the aerial itself, which was underground. Even though the L-shaped 'aerial' was 14 miles by 7 miles in length, it radiated maybe one hundred watts or so out of the one million watts driving it. Very inefficient.

Experiments have shown that it is possible to modulate the electron density in a patch of Earth's ionosphere by means of much higher frequency radio waves. These higher frequencies heat the patch which changes its electrical impedance. By varying the impedance in this way, you can generate extremely low-frequency radio waves, using the ionosphere itself as the aerial. I am presuming this is what the Navy is doing now.

The HAARP installation in Alaska can be used to generate ELF by means ionospheric heating. One of HAARP's antennae consists of a very large, rectangular phased array of 10 MHz dipoles. The energy is transmitted vertically upward, where it heats a comparatively-sized patch of ionosphere directly overhead. The ELF waves created in this way stay trapped between the Earth's surface and the ionosphere, which acts as a kind of waveguide and one large enough to efficiently carry the long-wavelength signal to all parts of the globe.

Another, very different approach which I believe was considered but dropped in favour of HAARP was to deliberately introduce minute differences in the relative phase between the eastern and western parts of the U.S. Power Grid. By varying the relative phase, the direction of energy flow can modulated accordingly. Utilities buy and sell power all the time and use a similar technique to accept or to provide power from/to elsewhere. This is a highly simplified picture of course, but basically that's what they do. Sink or source, with the entire U.S. Grid acting as the transmitter/aerial.

A VLF-radio hobbyist friend of mine who lives in Finland can easily detect minute changes in the U.S. power grid using fairly simple, home-brew equipment. If he can detect these changes halfway around the world, I'm sure submarines can too. For all I know the Navy might be using this technique as well.