His Majesty's Ship (HMS) is the prefix denoted to any commissioned vessels of the Stormwind Navy. In the Stormwind Navy, the prefix was originally denoted as, "His Majesty's Royal Ship" (HMRS), but was later shortened to "His Majesty's Ship" during Stormwind's massive naval expansion nearly 200 years ago.
All commissioned vessels hold this prefix, including auxiliary ships and submarines (Though for Submarines, Ship is sometimes informally replaced with Submarine)
This may also be applied to shore bases, which often take up a name of a historical vessel, usually with some form of significance towards the bases itself.