The United States Navy, United States Coast Guard, and United States National Oceanic and Atmospheric Administration (NOAA) use a hull classification symbol (sometimes called hull code or hull number) to identify their ships by type and by individual ship within a type. The system is analogous to the pennant number system that the Royal Navy and other European and Commonwealth navies use.
History
United States Navy The U.S. Navy began to assign unique Naval Registry Identification Numbers to its ships in the 1890s. The system was a simple one in which each ship received a number which was appended to its ship type, fully spelled out, and added parenthetically after the ship's name when deemed necessary to avoid confusion between ships. Under this system, for example, the battleship Indiana was USS Indiana (Battleship No. 1), the cruiser Olympia was USS Olympia (Cruiser No. 6), and so on. Beginning in 1907, some ships also were referred to alternatively by single-letter or three-letter codes—for example, USS Indiana (Battleship No. 1) could be referred to as USS Indiana (B-1) and USS Olympia (Cruiser No. 6) could also be referred to as USS Olympia (C-6), while USS Pennsylvania (Armored Cruiser No. 4) could be referred to as USS Pennsylvania (ACR-4). However, rather than replacing it, these codes coexisted and were used interchangeably with the older system until the modern system was instituted on 17 July 1920.
During World War I, the U.S. Navy acquired large numbers of privately owned and commercial ships and craft for use as patrol vessels, mine warfare vessels, and various types of naval auxiliary ships, some of them with identical names. To keep track of them all, the Navy assigned unique identifying numbers to them. Those deemed appropriate for patrol work received section patrol numbers (SP), while those intended for other purposes received "identification numbers", generally abbreviated "Id. No." or "ID;" some ships and craft changed from an SP to an ID number or vice versa during their careers, without their unique numbers themselves changing, and some ships and craft assigned numbers in anticipation of naval service were never acquired by the Navy. The SP/ID numbering sequence was unified and continuous, with no SP number repeated in the ID series or vice versa so that there could not be, for example, both an "SP-435" and an "Id. No. 435". The SP and ID numbers were used parenthetically after each boat's or ship's name to identify it; although this system pre-dated the modern hull classification system and its numbers were not referred to at the time as "hull codes" or "hull numbers," it was used in a similar manner to today's system and can be considered its precursor.Naval History and heritage Command Online Library of Selected Images (archived from the original at https://web.archive.org/web/20100329212007/http://www.history.navy.mil/photos/shusn-no/spid-no.htm).
United States Revenue Cutter Service and United States Coast Guard The United States Revenue Cutter Service, which merged with the United States Lifesaving Service in January 1915 to form the modern United States Coast Guard, began following the Navy's lead in the 1890s, with its cutters having parenthetical numbers called Naval Registry Identification Numbers following their names, such as (Cutter No. 1), etc. This persisted until the Navy's modern hull classification system's introduction in 1920, which included Coast Guard ships and craft.
United States Coast and Geodetic Survey
Like the U.S. Navy, the United States Coast and Geodetic Survey – a uniformed seagoing service of the United States Government and a predecessor of the National Oceanic and Atmospheric Administration (NOAA) – adopted a hull number system for its fleet in the 20th century. Its largest vessels, "Category I" oceanographic survey ships, were classified as "ocean survey ships" and given the designation "OSS". Intermediate-sized "Category II" oceanographic survey ships received the designation "MSS" for "medium survey ship," and smaller "Category III" oceanographic survey ships were given the classification "CSS" for "coastal survey ship." A fourth designation, "ASV" for "auxiliary survey vessel," included even smaller vessels. In each case, a particular ship received a unique designation based on its classification and a unique hull number separated by a space rather than a hyphen; for example, the third Coast and Geodetic Survey ship named Pioneer was an ocean survey ship officially known as USC&GS Pioneer (OSS 31).United States Department of State, United States Treaties and Other International Obligations, Volume 23, Part Four, Washington, D.C.:U.S. Government Printing Office, 1972, p. 3612. The Coast and Geodetic Surveys system persisted after the creation of NOAA in 1970, when NOAA took control of the Surveys fleet, but NOAA later changed to its modern hull classification system.
United States Fish and Wildlife Service
The Fish and Wildlife Service, created in 1940 and reorganized as the United States Fish and Wildlife Service (USFWS) in 1956, adopted a hull number system for its fisheries research ships and patrol vessels. It consisted of "FWS" followed by a unique identifying number. In 1970, NOAA took control of the seagoing ships of the USFWS's Bureau of Commercial Fisheries, and as part of the NOAA fleet they were assigned new hull numbers beginning with "FRV," for Fisheries Research Vessel, followed by a unique identifying number. They eventually were renumbered under the modern NOAA hull number system.
United States Lighthouse Service Vessels commissioned by the United States Lighthouse Service (USLHS) were originally not given unique names or hull numbers. Instead, names were exchanged when a new vessel was assigned to a station. Lightships first received the hull code "LS" before being replaced by "LV" (lightvessel). When the USLHS was absorbed by the U.S. Coast Guard in 1939, lightships were reassigned "WAL" for "anchored light" and "WLV" using the Coast Guard's "W" prefix. Finally, all lightships took the "WLV" designation after 1965 until the entire fleet was retired.
The modern hull classification system
United States Navy
The U.S. Navy instituted its modern hull classification system on 17 July 1920, doing away with section patrol numbers, "identification numbers", and the other numbering systems described above. In the new system, all hull classification symbols are at least two letters; for basic types the symbol is the first letter of the type name, doubled, except for aircraft carriers.
The combination of symbol and hull number identifies a modern Navy ship uniquely. A heavily modified or re-purposed ship may receive a new symbol, and either retain the hull number or receive a new one. For example, the heavy gun cruiser was converted to a gun/missile cruiser, changing the hull number to CAG-1. Also, the system of symbols has changed a number of times both since it was introduced in 1907 and since the modern system was instituted in 1920, so ships' symbols sometimes change without anything being done to the physical ship.Derdall and DiGiulian, (section: Nomenclature history)
Hull numbers are assigned by classification. Duplication between, but not within, classifications is permitted. Hence, CV-1 was the aircraft carrier and BB-1 was the battleship .
Ship types and classifications have come and gone over the years, and many of the symbols listed below are not presently in use. The Naval Vessel Register maintains an online database of U.S. Navy ships showing which symbols are presently in use.
After World War II until 1975, the U.S. Navy defined a "frigate" as a type of surface warship larger than a destroyer and smaller than a cruiser. In other navies, such a ship generally was referred to as a "flotilla leader", or "destroyer leader". Hence the U.S. Navy's use of "DL" for "frigate" prior to 1975, while "frigates" in other navies were smaller than destroyers and more like what the U.S. Navy termed a "destroyer escort", "ocean escort", or "DE". The United States Navy 1975 ship reclassification of cruisers, frigates, and ocean escorts brought U.S. Navy classifications into line with other nations' classifications, at least cosmetically in terms of terminology, and eliminated the perceived "cruiser gap" with the Soviet Navy by redesignating the former "frigates" as "cruisers".
Military Sealift Command If a U.S. Navy ship's hull classification symbol begins with "T-", it is part of the Military Sealift Command, has a primarily civilian crew, and is a United States Naval Ship (USNS) in non-commissioned service – as opposed to a commissioned United States Ship (USS) with an all-military crew.
United States Coast Guard If a ship's hull classification symbol begins with "W", it is a commissioned cutter of the United States Coast Guard. Until 1965, the Coast Guard used U.S. Navy hull classification codes, prepending a "W" to their beginning. In 1965, it retired some of the less mission-appropriate Navy-based classifications and developed new ones of its own, most notably WHEC for "high endurance cutter" and WMEC for "medium endurance cutter".
National Oceanic and Atmospheric Administration The National Oceanic and Atmospheric Administration (NOAA), a component of the United States Department of Commerce, includes the National Oceanic and Atmospheric Administration Commissioned Officer Corps (or "NOAA Corps"), one of the eight uniformed services of the United States, and operates a fleet of seagoing research and survey ships. The NOAA fleet also uses a hull classification symbol system, which it also calls "hull numbers," for its ships.
After NOAA took over the former fleets of the U.S. Coast and Geodetic Survey and the U.S. Fish and Wildlife Service Bureau of Commercial Fisheries in 1970, it initially retained the Coast and Geodetic Survey's hull-number designations for its survey ships and adopted hull numbers beginning with "FRV", for "Fisheries Research Vessel", for its fisheries research ships. It later adopted a new system of ship classification, which it still uses today. In its modern system, the NOAA fleet is divided into two broad categories, research ships and survey ships. The research ships, which include oceanographic and fisheries research vessels, are given hull numbers beginning with "R", while the survey ships, generally hydrographic survey vessels, receive hull numbers beginning with "S". The letter is followed by a three-digit number; the first digit indicates the NOAA "class" (i.e., size) of the vessel, which NOAA assigns based on the ship's gross tonnage and horsepower, while the next two digits combine with the first digit to create a unique three-digit identifying number for the ship.
Generally, each NOAA hull number is written with a space between the letter and the three-digit number, as in, for example, or .Wertheim, The Naval Institute Guide to Combat Fleets of the World, 15th Edition: Their Ships, Aircraft, and Systems, p. 1005.
Unlike in the U.S. Navy system, once an older NOAA ship leaves service, a newer one can be given the same hull number; for example, "S 222" was assigned to , then assigned to NOAAS Thomas Jefferson (S 222), which entered NOAA service after Mount Mitchell was stricken.
United States Navy hull classification codes
The U.S. Navy's system of alpha-numeric ship designators, and its associated hull numbers, have been for several decades a unique method of categorizing ships of all types: combatants, auxiliaries and district craft. Although considerably changed in detail and expanded over the years, this system remains essentially the same as when formally implemented in 1920. It is a very useful tool for organizing and keeping track of naval vessels, and also provides the basis for the identification numbers painted on the bows (and frequently the sterns) of most U.S. Navy ships.