JP 3-50 National Search and Rescue Manual Vol I - US Navy

location of small SOFAR devices detonating at predetermined
depths underwater. SOFAR nets are effective only in ocean
depths greater than the continental shelves (600 ft). Land
masses, including underwater sea mounts, will block the SOFAR
sound signals.
a. SOFAR devices may be released by aircraft, vessels,
or boats experiencing difficulties, or by survivors adrift on
the ocean; if time does not permit release before the
distressed craft ditches or sinks, a device may automatically
arm itself at approximately 800 feet and detonate between
2,400 and 4,000 feet. One station can obtain a line of
position (LOP) and an approximate range on each signal. Two
stations can cross LOPs to obtain a fix with an accuracy of
approximately 2 miles.
b. SMCs can query the SOFAR net any time a craft known
to carry a SOFAR device is missing. If a craft is definitely
overdue, the SOFAR net can search its recordings for SOFAR
signals from the last contact with the distressed craft to the
present, since survivors may have SOFAR devices in rafts as
well as in their vessel.
c. SAR aircraft carrying SOFAR devices can use them in
conjunction with SOFAR stations to maintain a constant bearing
with a distressed craft. When a SAR aircraft arrives on
scene, the SOFAR net may be able to vector it directly to the
SOFAR datum. The SAR aircraft may also be able to release a
SOFAR device at a distress scene where a lack of navigational
aids prevents accurately fixing the distress position.
8. The High-Frequency Direction-Finding (HFDF) net has a
frequency range between 2000 kHz and 30,000 kHz, and covers
both the Atlantic and the Pacific oceans. This net is alerted
when there is a reasonable expectation of locating the
distressed craft. To alert, SMCs provide certain information,
outlined by Navy OPNAVINST C2520.1 series and Coast Guard
COMDTINST
2-13