Why does Golding use a warship as the rescuing agent of the boys?

Golding might have used a warship to rescue the boys because this would facilitate the adult who rescued them be a person of higher authority, e.g. a Navel Officer would be a greater sign of dominance rather then a civilian.

On the other hand it could be seen as a form of irony, either the boys, who were waring against each other, were rescued by a symbol of war. Or that because the whole of the novel is an analogy for the beginning of the Second World War then to have them belittled by a military figure is, again, ironic.