Why use Amphibious Ready Group rather than Marine Amphibious Unit as a formation name?
Short answerThe suggested explanation concerns the impression of the words: group evokes a carrier battle group, while ready advertises deployability. The exchange does not document the organizational change assumed in the question.
NotesThe question frames ARG terminology as a replacement for Marine Amphibious Unit. The answer concentrates on the impression conveyed by the words: group resembles carrier battle group, and ready suggests immediate operational usefulness. A comparison with the Battle Cruiser Fleet and Grand Fleet questions how much a formation's imposing name tells a reader about its actual scale. The exchange concerns naming and presentation, without establishing the administrative history behind the question's premise.