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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 battleshipIndiana was USS Indiana (Battleship No. 1), the cruiserOlympia 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 never were 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.
United States Revenue Cutter Service and United States Coast Guard
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" oceanographicsurvey 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). 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.
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 USS Boston 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.
Hull numbers are assigned by classification. Duplication between, but not within, classifications is permitted. Hence, CV-1 was the aircraft carrierUSS Langley and BB-1 was the battleship USS Indiana.
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".
If a ship's hull classification symbol begins with "W", it is a ship 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".
After NOAA took over the former Coast and Geodetic Survey fleet in 1970 along with research vessels of other government agencies, it adopted a new system of ship classification. In its 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.
Unlike the Navy, once an older NOAA ship leaves service, a newer one can be given the same hull number; for example, "S 222" was assigned to NOAAS Mount Mitchell, 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. Though 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.
The ship designator and hull number system's roots extend back to the late 1880s, when ship type serial numbers were assigned to most of the new-construction warships of the emerging "Steel Navy". During the course of the next thirty years, these same numbers were combined with filing codes used by the Navy's clerks to create an informal version of the system that was put in place in 1920. Limited usage of ship numbers goes back even earlier, most notably to the "Jeffersonian Gunboats" of the early 1800s and the "Tinclad" river gunboats of the Civil War Mississippi Squadron.
It is important to understand that hull number letter prefixes are not acronyms, and should not be carelessly treated as abbreviations of ship type classifications. Thus, "DD" does not stand for anything more than "Destroyer". "SS" simply means "Submarine". And "FF" is the post-1975 type code for "Frigate."
The hull classification codes for ships in active duty in the United States Navy are governed under Secretary of the Navy Instruction 5030.8B (SECNAVINST 5030.8B).
Warships are designed to participate in combat operations.
The origin of the two-letter code derives from the need to distinguish various cruiser subtypes.
Heavy gun-armed vessel
armored (1921-1931) heavy (1931-)
battle (prior to 1961) command
aviation or voler
Aircraft carrier type
Aircraft carriers are ships designed primarily for the purpose of conducting combat operations by aircraft which engage in attacks against airborne, surface, sub-surface and shore targets. Contrary to popular belief, the "CV" hull classification symbol does not stand for "carrier vessel". "CV" derives from the cruiser designation, with the v for French voler, "to fly". Aircraft carriers are designated in two sequences: the first sequence runs from CV-1 USS Langley to the very latest ships, and the second sequence, "CVE" for escort carriers, ran from CVE-1 Long Island to CVE-127 Okinawa before being discontinued.
Surface combatants are ships which are designed primarily to engage enemy forces on the high seas. The primary surface combatants are battleships, cruisers and destroyers. Battleships are very heavily armed and armored; cruisers moderately so; destroyers and smaller warships, less so. Before 1920, ships were called "<type> no. X", with the type fully pronounced. The types were commonly abbreviated in ship lists to "B-X", "C-X", "D-X" et cetera--for example, before 1920, USS Minnesota would have been called "USS Minnesota, Battleship number 22" orally and "USS Minnesota, B-22" in writing. After 1920, the ship's name would have been both written and pronounced "USS Minnesota (BB-22)". In generally decreasing size, the types are:
DEG: Guided Missile Ocean Escort (abolished 30 June 1975)
DER: Radar Picket Destroyer Escort (abolished 30 June 1975) There were two distinct breeds of DE, the World War II Destroyer Escorts (some of which were converted to DERs) and the postwar DE/DEG classes, which were known as Ocean Escorts despite carrying the same type symbol as the World War II Destroyer Escorts. All DEs, DEGs, and DERs were reclassified as FFs, FFGs, or FFRs, 30 June 1975.
DLG: Frigate, Guided Missile (abolished 30 June 1975)
DLGN: Frigate, Guided Missile, Nuclear-Propulsion (abolished 30 June 1975) The DL category was established in 1951 with the abolition of the CLK category. CLK 1 became DL 1 and DD 927-930 became DL 2-5. By the mid-1950s the term Destroyer Leader had been dropped in favor of Frigate. Most DLGs and DLGNs were reclassified as CGs and CGNs, 30 June 1975. However, DLG 6-15 became DDG 37-46. The old DLs were already gone by that time. Only applied to USS Bainbridge.
FFT: Frigate (Reserve Training) (retired) The FF, FFG, and FFR designations were established 30 June 1975 as new type symbols for ex-DEs, DEGs, and DERs. The first new-built ships to carry the FF/FFG designation were the Oliver Hazard Perry-classfrigates. In January 2015, it was announced that the LCS ship types would be redesignated as FF.
LCS: Littoral Combat Ship In January 2015, the Navy announced that the up-gunned LCS will be reclassified as a frigate, since the requirements of the SSC Task Force was to upgrade the ships with frigate-like capabilities. Hull designations will be changed from LCS to FF; existing LCSs back-fitted with modifications may also earn the FF label. The Navy is hoping to start retrofitting technological upgrades onto existing and under construction LCSs before 2019.
Submarines are all self-propelled submersible types (usually started with SS) regardless of whether employed as combatant, auxiliary, or research and development vehicles which have at least a residual combat capability. While some classes, including all diesel-electric submarines, are retired from USN service, non-U.S. navies continue to employ SS, SSA, SSAN, SSB, SSC, SSG, SSM, and SST types. With the advent of new Air Independent Propulsion/Power (AIP) systems, both SSI and SSP are used to distinguish the types within the USN, but SSP has been declared the preferred term. SSK, retired by the USN, continues to be used colloquially and interchangeably with SS for diesel-electric attack/patrol submarines within the USN, and, more formally, by the Royal Navy and British firms such as Jane's Information Group.
Patrol combatants are ships whose mission may extend beyond coastal duties and whose characteristics include adequate endurance and sea keeping, providing a capability for operations exceeding 48 hours on the high seas without support. This notably included Brown Water Navy/Riverine Forces during the Vietnam War. Few of these ships are in service today.
Amphibious warfare vessels include all ships having organic capability for amphibious warfare and which have characteristics enabling long duration operations on the high seas. There are two classifications of craft: amphibious warfare ships which are built to cross oceans, and landing craft, which are designed to take troops from ship to shore in an invasion.
AGHS: Patrol Combatant Support Ship--Ocean or Inshore
Although technically an aircraft, pre-World War II rigid airships (e.g., zeppelins) were treated like commissioned surface warships and submarines, flew the U.S. ensign from their stern and carried a United States Ship (USS) designation. Non-rigid airships (e.g., blimps) continued to fly the U.S. ensign from their stern, but were always considered to be primarily aircraft.
Support ships are not designed to participate in combat, and are generally not armed. For ships with civilian crews (owned by and/or operated for Military Sealift Command and the Maritime Administration), the prefix T- is placed at the front of the hull classification.
Support ships are designed to operate in the open ocean in a variety of sea states to provide general support to either combatant forces or shore based establishments. They include smaller auxiliaries which, by the nature of their duties, leave inshore waters.
Service craft are navy-subordinated craft (including non-self-propelled) designed to provide general support to either combatant forces or shore-based establishments. The suffix "N" refers to non-self-propelled variants.
United States Navy Designations (Temporary) are a form of U.S. Navy ship designation, intended for temporary identification use. Such designations usually occur during periods of sudden mobilization, such as that which occurred prior to, and during, World War II or the Korean War, when it was determined that a sudden temporary need arose for a ship for which there was no official Navy designation.
During World War II, for example, a number of commercial vessels were requisitioned, or acquired, by the U.S. Navy to meet the sudden requirements of war. A yacht acquired by the U.S. Navy during the start of World War II might seem desirable to the Navy whose use for the vessel might not be fully developed or explored at the time of acquisition.
On the other hand, a U.S. Navy vessel, such as the yacht in the example above, already in commission or service, might be desired, or found useful, for another need or purpose for which there is no official designation.
IX: Unclassified Miscellaneous Auxiliary Ship, for example yacht Chanco acquired by the U.S. Navy on 1 October 1940. It was classified as a minesweeperAMc-5, but instead, mainly used as a patrol craft along the New England coast. When another assignment came, and it could not be determined how to classify the vessel, it was redesignated IX-175 on 10 July 1944.
Numerous other U.S. Navy vessels were launched with a temporary, or nominal, designation, such as YMS or PC, since it could not be determined, at time of construction, what they should be used for. Many of these were vessels in the 150 to 200 feet length class with powerful engines, whose function could be that of a minesweeper, patrol craft, submarine chaser, seaplane tender, tugboat, or other. Once their destiny, or capability, was found or determined, such vessels were reclassified with their actual designation.
National Oceanic and Atmospheric Administration hull codes
R: Research ships, including oceanographic and fisheries research ships
S: Survey ships, including hydrographic survey ships
^This odd entry is not recognised by the U.S. Naval Vessel Register, and appears only in MIL-STD-2525A: Common Warfighting Symbology (15 December 1996) and later editions (MIL-STD-2525B: Common Warfighting Symbology (30 January 1999) and MIL-STD-2525C: Common Warfighting Symbology (17 November 2008)). It seems to refer to some kind of nuclear-powered submarine used by Special Operations Forces.
^Russia still employs several SSA and SSAN class submarines like the Delta Stretch as well as one SST, China has older SSB and SSG types such as the Golf and Mod Romeo classes, and North Korea has built many SSCs and SSMs. See 2007-2008 Janes Fighting Ships.
Wertheim, Eric. The Naval Institute Guide to Combat Fleets of the World, 15th Edition: Their Ships, Aircraft, and Systems. Annapolis, Maryland: Naval Institute Press, 2007. ISBN978-1-59114-955-2. ISSN1057-4581.
Friedman, Norman. U.S. Small Combatants, Including PT-Boats, Subchasers, and the Brown-Water Navy: An Illustrated Design History. Annapolis, Md: Naval Institute Press, 1987. ISBN0-87021-713-5.