November 19, 2007: The U.S.
Navy has developed a system for contacting nuclear subs that, normally, could
not be contacted until the boat came close to the surface and poked a radio
antenna above the surface. The new system is called Deep Siren (or
"tactical paging system"), and provides a partial solution to the
problem of contacting a submerged sub. The system consists of a disposable
buoy, that is dropped in the water, usually by an aircraft, in the general area
(within about 80 kilometers) where the sub is believed to be. The buoy sends
out an acoustic signal that U.S. subs are equipped to pick up. This coded
message either orders the sub to get a radio antenna above water and call home,
or simply delivers a brief message. The buoy also has a satellite telephone
capability, so that additional messages can be sent to the sub. For the sub, the
messages are strictly one way. In the past, the only way to "page"
submerged subs was via a large, shore based, low frequency, transmission
system. This system was less reliable than the new one, although it had a much
longer range.
Deep Siren will also be useful for American carrier task
forces, which are usually accompanied by at least one SSN (nuclear attack sub.)
With a system like this, details are usually classified, and the range of Deep
Siren is probably longer than the press releases indicated. Whales use a
similar low frequency transmission system, and these messages carry for
hundreds of kilometers. Another large mammal, the elephant, has also been found
to use very low frequency sounds to communicate, through the ground, rather
than the water, for long distances. When you want to send a message via dense
material, like water or earth, low frequency sounds work best.
