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 " SS " for steamship , 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 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 frigate s of the United States Navy . Today the common practice is to use a single prefix for all warship s of a nation ' s navy , and other prefixes for auxiliaries and ships of allied services , such as coast guard s . 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 number s — identification codes typically painted on the side of the ship . Each navy has its own system : the United States Navy uses hull classification symbol s , and the Royal Navy and other navies of Europe and the Commonwealth use pennant number s . These tables list both current and historical prefixes known to have been used . Notes and references . The designations for United Kingdom ships applied at the time of the British Empire , before the establishment of separate navies for the Dominions . In the Royal Netherlands Navy , " HNLMS " is the prefix in English , a translation of the Dutch original " Hr . Ms . " or " Zr . Ms . " . " Hr . Ms . " should preferably not be used in English - language documents ; nevertheless it is often seen on the World Wide Web . Until the moment a Dutch naval ship officially enters active service in the fleet , the ship ' s name is used without the prefix . Since King Willem - Alexander succeeded Queen Beatrix on 30 April 2013 , " Hr . Ms . " is replaced by " Zr . Ms . " . In Australia , the prefix NUSHIP is used to denote ships that have yet to be commissioned into the fleet . In the United States Navy , all prefixes other than " USS , " " USNS " , " USNV " , and " USRC " were made obsolete in 1901 when President Theodore Roosevelt signed into law a bill fixing American naval nomenclature . USRC was replaced by USCGC when the Revenue Cutter Service became the United States Coast Guard in 1915 . A United States ship that has not yet been commissioned in the Navy does not hold the title of USS , it holds the title of PCU ( Pre - commissioned unit ) . For example , say a shipyard is building a new aircraft carrier , the " Flattop " . From the date the keel is laid to the date it is commissioned , it is called the PCU " Flattop " . Only after it enters active service in the fleet and is commissioned will it be referred to as USS " Flattop " . By law , the U . S . Navy may not purchase foreign - built ships , but it may lease them as United States Naval Vessels . When it is stricken from the fleet list , a ship typically has the prefix " ex - " added to its name , to distinguish it from any active ships bearing the same name . For example , after USS " Constellation " ( CV - 64 ) was retired in 2003 , she became referred to as ex - " Constellation " . Note that while calling a US ship " the USS " Flattop " " may make grammatical sense , the preliminary article " the " is discouraged by nearly all style guides , and the U . S . Navy . The U . S . Navy uses ship names without article , except for USS " The Sullivans " , named for the five Sullivan brothers , all lost at sea during World War II . Its British equivalent ( " the HMS " Flattop " " ) is also discouraged , since " the Her Majesty ' s Ship " would be grammatically incorrect . Civilian ships naming . In 1939 , the British Ministry of Shipping adopted a standard naming system whereby all merchant ships ordered to be built in Britain to Government account , except very small ship types , would be given the prefix " Empire " to their name . This applied to ships acquired through purchase , requisition , or taken in prize , with some exceptions . It also applied to older ships acquired from the USA , modern ships acquired on Lease / Lend arrangements , salved and refitted ships , and captured enemy ships . In science fiction . In the fictional Star Trek universe , the United Federation of Planets uses the prefix " USS " for its starships . It stands for " United Space Ship " or " United Star Ship " .