The speaker feels trapped aboard something they never chose. The opening line, "who is carrying us to war," has no clear subject, which makes the threat feel faceless: someone, somewhere, is steering everyone toward violence. The speaker's response is to block out the news by stopping up their ears, and the poem calls this "the first act of hostility." That's a striking turn. Refusing to listen is treated as its own small act of aggression, or perhaps the first casualty of a war that has already begun.
The final lines are bleaker still. "The land is sunk" suggests a world already lost, while the captain alone has "found a finite bed," which could mean a grave, or a private comfort the rest don't get. The title, "Life preserver," sits ironically over all of this, since nothing here seems to save anyone. The mood is dread, helplessness, and numbed withdrawal.