Trapped in a sub at the bottom of the ocean. Can murder be legal or morally acceptable?

Obviously inspired by the news of the day. Imagine a scenario in which multiple people are trapped with limited air, facing guaranteed death if they are not rescued soon, due to limited air supplies. Would it be morally acceptable for the group to kill one or more of their companions, so that the others might have a better chance to live? Do other factors affect the morality of this decision? What would a court think if the rescue was successful? Would it matter if the murder was strictly necessary, had the timeline of the rescue been knowable?