The USS Constitution, RMS Titanic, and SS Great Britain are among the most famous ships in history. In addition to their historical significance, all three share a common detail—their names begin with a letter code called a ship prefix.
Numerous civilian and military vessels have used ship prefixes in their name. These codes, typically two or three letters, convey information such as the ship’s type, nationality, or owner. Discover the meaning of these prefixes and how they have been used throughout naval history to showcase maritime tradition and innovation.
The practice of adding prefixes to a ship’s name has existed for hundreds of years. Traditionally, ship prefixes identified one of three elements: the ship’s affiliation, method of propulsion, or purpose.
The Royal Navy was among the first to adopt the practice of using ship prefixes. Its original purpose was to designate the ship’s British affiliation and relationship to the crown. Early Royal Navy ships were prefixed HBMS, which stood for His Britannic Majesty’s Ship, before dropping the B and adopting the more well-known HMS.
When the United States Navy was formed in 1775, it adopted a similar convention. The prefix USS—United States Ship—is explicitly used to identify U.S. Navy warships while under commission.
According to U.S. Navy naming conventions, a Navy ship loses the USS prefix after decommissioning. For example, USS Enterprise (CVN-65) used the prefix from 1961 to her decommissioning in 2017, after which she became known as simply Enterprise.
Today, using ship prefixes to designate affiliations or ownership entities is primarily a military naming convention. Most armed forces use them to identify a naval or coast guard vessel. Some examples of commonly used military affiliation prefixes include:
| Prefix | Meaning | Usage |
| HMS | His/Her Majesty’s Ship | His/Her Majesty’s Ship, most famously used by the British Royal Navy. Commonwealth countries use variants to distinguish them from British ships, such as HMAS in Australia, HMCS in Canada, and HMNZS in New Zealand. |
| JS | Japanese Ship | The Japanese Maritime Self-Defense Force uses the JDS (Japanese Defense Ship) prefix. Older ships use the earlier prefix. |
| RMS | Royal Mail Service | While contracted by the United Kingdom government, RMS ships were owned by private companies and operated by civilian crews to transport mail between British colonies. |
| USCGC | United States Coast Guard Cutter | Designates commissioned U.S. Coast Guard ships. |
| USS | United States Ship | Designates commissioned U.S. Navy ships. |
Many civilian vessels use ship prefixes to designate their propulsion method. The SS prefix, which appeared in the 19th century, is one of the earliest and most famous examples. It designated steam-powered craft, then at the cutting edge of naval technology.
Originally, SS specifically referred to single-screw steamships, a specific type of steamship fitted with one propeller. SS Great Britain, launched in 1843, is a notable historical example. Over time, as the prefix entered everyday use, it eventually became a shorthand for steamship and included later vessels with multiple propellers.
Following the tradition established by the SS prefix, more modern and advanced vessels used similar designations to explain their mode of propulsion. Prominent examples of this naming method include:
| Prefix | Meaning | Example |
| GTS | Gas turbine ship | |
| MS MV | Motor ship Motor vessel | Used on vessels powered by a gasoline or diesel combustion engine, such as MV American Tern. |
| NS | Nuclear ship | NS Savannah, the world’s first nuclear-powered cargo ship. |
| SV | Sailing vessel | |
| TSS | Twin-screw steamship |
Many ships, such as fishing boats or scientific research ships, used prefixes to designate their purpose instead of an owner or propulsion system.
This naming convention first appeared in the early to mid-20th century and is sometimes retroactively used on vessels that didn’t formally use it in their name. For example, Belgica, a steamship built in 1884 that participated in Antarctic research expeditions, is sometimes referred to as RV Belgica.
Most ship prefixes used to denote the ship’s purpose have civilian applications. Common examples include:
| Prefix | Meaning | Example |
| CS | Cable ship Cable-laying ship | CS Chamarel, which was destroyed in a fire off the Namibian coast in 2012. |
| FV | Motor ship Motor vessel | FV Northwestern, as made famous by the TV show Deadliest Catch |
| RV RSV | Research vessel Research survey vessel | |
| TB | Sailing vessel | |
| TS TV | Training ship Training vessel |
Dozens of different ship prefixes have been created over the years, with many meanings changing or evolving. Here’s a guide to the most commonly confused ship prefixes.
In the past, TS referred to a turbine steamship, such as TS King George V. Today, it is more commonly used to denote a training ship.
The easiest way to tell the two apart is to check the ship’s design; if it has funnels for exhausting steam, it is likely a steamship. If it is a modern vessel, it’s most likely a training ship.
The most common purpose of the SY prefix is to denote a sailing yacht, like the SY Maltese Falcon. However, the prefix was also commonly used in the early 20th century to designate a steam yacht.
While both ship types often had sails, only steam yachts had a steam exhaust funnel.
Two common ship prefixes in U.S. Navy service are United States Ship (USS) and United States Naval Ship (USNS). Despite the close designations, they refer to vessels with different missions and purposes.
The easiest way to differentiate USS from USNS ships is to check the crew and onboard weapons. United States Ships are warships armed with large weapon systems and crewed by uniformed sailors, whereas USNS vessels are civilian-crewed and have few or no onboard weapons.
Ship prefixes are one of many maritime traditions, and the long history of these naming conventions has evolved alongside naval technology. While they were always intended as a convenient way to understand a ship’s origin and purposes, their meaning and significance vary by region.
Some prefixes, such as USS and HMS, are formally regulated by military law or international standards. Others, like SS and MV, are more of a tradition born from their respective eras’ industry standards conventions.
Corentin’s passion for the boating and yachting industry was ignited early on, fueled by the prestigious Salon Nautique International de Paris and the Cannes Yachting Festival. Now a seasoned writer, he channels his expertise into every piece, whether he’s showcasing the latest in luxury yachts or breaking down marine tech innovations. While boating and yachting are a primary focus, Corentin’s versatility is reflected in his work on automotive trends, home improvement, personal finance, and cutting-edge technology.