Editing Hull classification symbol (section)

=== 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.