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

1. Where sea current, tidal current, and wind-driven currents can
greatly influence datum calculation, an electronic datum
marker should be deployed before beginning the first search
leg. Where multiple SRUs are assigned for large area
searches, this responsibility should be given to the SRU
assigned the search area in which datum is located, assuming
the SRU has a highly accurate navigation system. The SRU
should report to the OSC on the exact position, time of
insertion, expected battery life, and radio frequency of the
marker.
2. For sector searches, any type of marking device that can be
located visually or electronically may be used as a datum
marker. Smoke floats, life ring lights, fishing floats, and
Personal Flotation Devices (PFDs) have all been used
successfully.
3. Over a desert or water area, datum may be
6-2