HMS

HMS is a ship prefix used for commissioned warships of the Royal Navy (and, historically, for ships of other Commonwealth navies). It stands for Her Majesty's Ship or His Majesty's Ship, depending on the reigning monarch. The prefix signals that the vessel is owned by the Crown and subject to naval command, rather than being a private or civilian vessel. The practice began in the early modern period and became standard for Royal Navy ships by the 18th century.

Ships bearing the prefix include aircraft carriers, destroyers, frigates, submarines, and auxiliary vessels. A ship is addressed as HMS Name in official records and in communication. The prefix is retained for the life of the ship while it is commissioned, and is not used for merchant ships or private fleets.

Notable examples include HMS Victory, Nelson's flagship at the Battle of Trafalgar; HMS Queen Elizabeth, the lead ship of the Queen Elizabeth-class aircraft carriers; and HMS Hood, a prominent battlecruiser of the 20th century. In other Commonwealth navies, different prefixes are used, such as HMCS (Canada), HMAS (Australia), and HMNZS (New Zealand).

Today the prefix remains in use with current Royal Navy vessels; it can switch between "Her" and "His" as the monarch changes. The term is a convention of naval nomenclature rather than a legal title.