As U.S. Military Protocol it is very rare that a Lower Rank/Grade U.S. Military Service Member (Escort Officer) accompanies the Deceased U.S. Military Service Member's coffin (Dignified Transfer), unless specifically requested before death--which was the case in this instance.
The trident which Junior is wearing is indicative of being a member of the U.S. Navy SEALS (SEa Air Land). It is also known as a Budweiser.
Combat Air Controller directs the landing and take-off of aircraft, especially in makeshift airfields. It also coordinates the targeting of ordinance from close air support.
The instrument Steve and Danny throw overboard to look for the missing feet is a Teledyne Bethos (formerly Datasonics) SIS-1600 series side scan towed sonar array.
The boat Steve and Danny are on is the "Huki Pono" owned by Sea Engineering, Inc. of Honolulu, Hawaii. This 43-foot craft is used to support diving and marine surveying operations, and was built in 1985 by Delta Marine in Seattle, Washington.