This is amaintenancecategory, used formaintenance of the Wikipedia project. It is not part of the encyclopedia and containsnon-article pages, or groups articles by status rather than subject. Do not include this category in content categories (except foreponymous maintenance categories).

This is atracking category. It builds and maintains a list of pages primarily for the sake of the list itself. They are not part of theencyclopedia's categorization scheme.

This is a maintenance category for tracking articles that use{{Ship in active service}} without specifying a date. It may sometimes be empty, but should not be considered useless. SeeWikiProject Ships for more information.