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RMS Titanic, USS Indianapolis, HMS Victory—you've probably noticed that many ship names come with a few letters in front of them.
These prefixes may seem random, but in reality, each is an initialism that identifies the specific type or role of the ship. In civilian vessels, the 'SS' designation is among the most common.
The Evolution of U.S. Ship Designations
The 'SS' label originated in the mid-1800s, when steam-powered ships began replacing the Age of Sail. Shipbuilders sought a way to distinguish these modern vessels, and the 'SS' abbreviation for 'steamship' became the solution.
As naval technology advanced, so did the interpretation of what 'SS' actually stood for. Some 'SS' vessels were screw steamers or single-screw steamships (with 'screw' referring to the ship's propeller), while paddle steamers were often labeled 'PS,' and larger twin- and triple-screw steamships were designated as 'TSS' and 'TrSS,' respectively.
Theodore Roosevelt issued an executive order that helped standardize U.S. Navy vessel designations. | Heritage Images/GettyImagesNot all ships are civilian-operated. In the U.S., all Navy vessels carry the prefix 'USS,' standing for 'United States Ship.' This system was introduced by President Theodore Roosevelt through an executive order, which declared that ‘the official designation of vessels of war, and other vessels of the Navy of the United States, shall be the name of such vessel, preceded by the words, United States Ship, or the letters U.S.S., and by no other words or letters.’ Prior to this, ships were named according to various features such as their class, type, or rigging arrangements, without much consistency.
Ship Designations Globally
Other countries have their own specific ship prefixes. For example, ships in the UK's Royal Navy are marked with 'HMS' ('His or Her Majesty's Ship'), and other Commonwealth nations follow suit: Canada uses 'HMCS,' Australia uses 'HMAS,' and New Zealand uses 'HMNZS.'
The RMS 'Titanic.' | George Rinhart/GettyImagesThe 'Titanic' was assigned the 'RMS' prefix because, even though it was a commercial ship, it had been contracted to carry goods for the UK’s Royal Mail service. The term 'RMS' originally stood for 'Royal Mail Steamer,' though today it simply means 'Royal Mail Ship.' In contrast, British scientific ships bearing royal approval are designated 'RRS,' which stands for 'Royal Research Ship'—as seen with Sir Robert Falcon Scott’s Antarctic expedition vessel, RRS Discovery.
