Ship prefix

A ship prefix is a combination of letters, usually abbreviations, used in front of the name of a civilian or naval ship.

Prefixes for civilian vessels may either identify the type of propulsion, such as "PS" for paddle steamer, or purpose, such as "RV" for research vessel. Civilian prefixes are often used inconsistently, and frequently not at all. Sometimes a slash is used to separate the letters, as in "M/S".

Naval prefixes came into use as abbreviations for longer titles, such as "His/Her Majesty's Ship" in the British Royal Navy, abbreviated "H.M.S." and then "HMS". Earlier uses often included the type of vessel, as for instance "U.S.F." ("United States Frigate") for frigates of the United States Navy, that were eliminated by President Theodore Roosevelt's Executive order of 1907 making "United States Ship" (USS) the standard for the Navy's commissioned ships while in commission. In the United States Navy that prefix officially only applies while the ship is in active commission, with only the name used before or after a period of commission and for all vessels "in service" rather than commissioned status. Today the common practice is to use a single prefix for all warships of a nation's navy, and other prefixes for auxiliaries and ships of allied services, such as coast guards.

The use of ship prefixes is not universal; in particular neither the German Kriegsmarine nor the Imperial Japanese Navy used ship prefixes. Some English-language writers use prefixes like "DKM" (for "Deutsche Kriegsmarine") and "HIJMS" (for "His Imperial Japanese Majesty's Ship") or "IJN" (for "Imperial Japanese Navy", a translation of 大日本帝国海軍 dai-nippon teikoku kaigun) for consistency with "HMS" and "USS". Other writers follow the practice of the navy and omit any prefix.

From the 20th century onwards, most navies identify ships by hull numbers (pennant numbers)—identification codes typically painted on the side of the ship. Each navy has its own system: the United States Navy uses hull classification symbols, and the Royal Navy and other navies of Europe and the Commonwealth use pennant numbers.

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