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

Figure 6-1. En Route Searching
or speed of advance, on scene endurance, intended departure point and
time, and whether the vessel navbeacon is tuned and identified.
B. As SRUs arrive, the OSC should provide information on new
developments, search targets, search area designation, search
pattern(s), recommended common on scene altimeter setting, altitude and
track spacing, Commence Search Point (CSP), pertinent communications and
navigation information (IFF squawk, air-to-air TACAN channels, etc.),
traffic advisories, "operations normal" reporting times, check-in/check-out
procedures, and on scene weather.
C. Normally, the SMC will direct the SRU having the most accurate
navigation equipment to deploy a Datum Marker Buoy (DMB). The time and
position should be closely monitored and reported to the SMC. Datum
markers are useful for determining total water current, and serve as a
visual or electronic centerpoint for sector searches. An accurate datum
can be obtained by applying leeway to the marker position. Subsequent
markers should be deployed at the newly computed datum. SMC
coordination protects against two DMBs with the same frequency being
activated at the same time. However, on an urgent call, in the absence
of SMC instructions, the first SRU on scene should deploy a DMB on
arrival.