Ship Names and Prefixes: What Do “RMS” and Others Mean?

A ship prefix appears before a ship’s name and places it in a linguistic or historical context. Abbreviations such as “HMS,” “SS” and “RMS” offer clues about a ship’s tradition, service or type.

Prefix and ship name

The letters are usually written as part of the commonly used form of the name: the name Titanic thus becomes “RMS Titanic.” Depending on the language, era and institution, a prefix can have different meanings. An English abbreviation therefore often stands for a longer designation of function or affiliation. To understand it, it helps to read the abbreviation together with the name and know its expanded form.

Examples: HMS, SS, RMS and HMY

“HMS” stands for “Her Majesty’s Ship” or “His Majesty’s Ship” and designates a ship of the British Royal Navy. The form depends on how the monarch is addressed and is associated with service in the Royal Navy. “SS” means “Steam Ship”: the prefix refers to a steamship and is found particularly in ship names from the era when steam engines were the predominant means of propulsion.

“RMS” expands to “Royal Mail Ship.” In the case of the Titanic, it referred to the mail service on board; in addition to passengers, the ship carried mail. The abbreviation thus points to an operational role. “HMY” stands for “Her Majesty’s Yacht” or “His Majesty’s Yacht” and identifies a royal yacht.

Those interested in the Titanic can find more ships in the ships section and the ship archive. The article Ship registration and flag state explains which details relate to a ship’s registration and flag.

Prefixes and identification

A prefix is part of a ship’s name and its meaning. It should be distinguished from official registration and technical identifiers: call signs and MMSIs are used for radio identification, while the IMO number is a permanent identifier for an individual ship. According to the International Maritime Organization, this number remains unchanged throughout the ship’s entire lifetime, even if its flag, name, owner or type changes. Each of these details therefore answers a different question: the prefix explains a naming or service tradition, while registers and identifiers indicate a ship’s registration or identity.