Editing Hull classification symbol (section)

== 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|CA-69}} 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.<ref>Derdall and DiGiulian, (section: ''Nomenclature history'')</ref>

Hull numbers are assigned by classification. Duplication between, but not within, classifications is permitted. Hence, CV-1 was the [[aircraft carrier]] {{USS|Langley|CV-1|6}} and BB-1 was the battleship {{USS|Indiana|BB-1|6}}.

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 [[cruiser]]s, 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 [[United States Navy 1975 ship reclassification#The "cruiser gap"|"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 [[Ship commissioning|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 [[United States Coast Guard Cutter|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 ships and aircraft|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 ship]]s and adopted hull numbers beginning with "FRV", for "Fisheries Research Vessel", for its [[Fishery|fisheries]] [[research ship]]s. 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 [[Oceanography|oceanographic]] and fisheries research vessels, are given hull numbers beginning with "R", while the survey ships, generally [[hydrography|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 ton]]nage 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, {{ship|NOAAS|Nancy Foster|R 352}} or {{ship|NOAAS|Thomas Jefferson|S 222}}.<ref>Wertheim, ''The Naval Institute Guide to Combat Fleets of the World, 15th Edition: Their Ships, Aircraft, and Systems'', p. 1005.</ref>

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 {{ship|NOAAS|Mount Mitchell|S 222}}, then assigned to NOAAS ''Thomas Jefferson'' (S 222), which entered NOAA service after ''Mount Mitchell'' was stricken.