His Majesty's Ship

His or Her Majesty's Ship (HMS) is the title used for ships of the navy in some monarchies, either formally or informally. In the British Royal Navy, it refers to the King or Queen of the United Kingdom as appropriate at the time. In the Royal Swedish Navy, consequently, the prefix stands for (Hans or Hennes Majestäts Skepp).

Formerly, HBMS for His or Her Britannic Majesty's Ship was also used.

Submarines in Her Majesty's service have the prefix HM Submarine (sometimes abbreviated HMSm). Similarly, the Royal Yacht Britannia, which was a commissioned ship in the Royal Navy, was known as HMY Britannia. Otherwise all ships in the Royal Navy are known as HM Ships, though formerly when a distinction was made between three-masted ship-rigged ships and smaller vessels they would be called HM Frigate X, or HM Sloop Y.

The HMS prefix is also used by shore establishments which are commissioned "stone frigates" in the Royal Navy. Examples include HMS Excellent, which is a training school located on an island in Portsmouth Harbour, and HMS Vulcan, in Caithness in the Highland area of Scotland, which is established to test the design of nuclear power systems for use in submarines.

The sample ship name used by the Royal Navy is HMS Nonsuch[1]. This is a name that has been used in the past, but is not in use at present.

British government ships not in the Royal Navy have other designations, such as "RFA" for ships in the Royal Fleet Auxiliary.

Other Commonwealth Realms use a variation of the "HMS" designation. For example, Canada uses HMCS for "Her Majesty's Canadian Ship", Australia uses HMAS, and so forth. (See ship prefix for a list.)