So in an active war is a US war ship got sunk and sailors abandoned ship with their emergency radios but are stranded and holding on to burning debris, do you think they would be fair game to murder if they were trying to call to other US ships for rescue?
The definitive answer is "no."
The answers are available to anyone and everyone in the Geneva Conventions.
Second Geneva Convention (1949)
*Article 12:
“Members of the armed forces and other persons mentioned in Article 13, who are wounded or sick, as well as shipwrecked at sea, shall be respected and protected in all circumstances. They shall be treated humanely and cared for by the Party to the conflict in whose power they may be, without any adverse distinction founded on sex, race, nationality, religion, political opinions, or any other similar criteria. Any attempts upon their lives, or violence to their persons, shall be strictly prohibited; in particular, they shall not be murdered or exterminated, subjected to torture or biological experiments; they shall not wilfully be left without medical assistance and care, nor shall conditions be created to cause their death.”
*Article 13 (defines who is covered):
“The present Convention shall apply to the wounded, sick and shipwrecked members of armed forces at sea, as well as to members of the crews of the merchant marine and the crews of civil aircraft of the Parties to the conflict, who do not benefit by more favourable treatment under any other provisions of international law.”