Hull classification symbol
The United States Navy uses hull classification symbols to identify the types of its ships. See also pennant number, a somewhat analogous system used by the Royal Navy and some European navies.The combination of symbol and hull number identify a modern Navy ship uniquely. A heavily modified or repurposed ship may receive a new symbol, and either retain the hull number or receive a new one. Also, the system of symbols has changed a number of times since it was introduced in 1907, so ships' symbols sometimes change without anything being done to the physical ship.
Many of these symbols are not presently in use.
Warships
Warships are designed to participate in combat operations.Aircraft Carrier Type
All ships designed primarily for the purpose of conducting combat operations by aircraft which engage in attacks against airborne, surface, sub-surface and shore targets. "CV" is from the original description, "Cruiser, Aviation" -- CA was already in use for "Cruiser, Armored".Surface Combatant Type
Large, heavily armed, surface ships which are designed primarily to engage enemy forces on the high seas.
A word about the DE type symbol is in order here. 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 WWII Destroyer Escorts. All DEs, DEGs, and DERs were reclassified as FFs, FFGs, or FFRs, 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.
The FF, FFG, and FFR designations were established 30 June 1975 as new type symbols for ex-DEs, DEGs, and DERs.Submarine Type
All self-propelled submersible types regardless of whether employed as combatant, auxiliary, or research and development vehicles which have at least a residual combat capability.
There have been several other submarine designations which did not begin with SS, included here for completeness:
(Note: SSP, ASSP, APSS, and LPSS were all the same type, redesignated over the years.)
Patrol Combatant Type
Combatants 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.Amphibious Warfare Type
All ships having organic capability for amphibious assault and which have characteristics enabling long duration operations on the high seas.Combat Logistics Type
Ships which have the capability to provide underway replenishment to fleet units.Mine Warfare Type
All ships whose primary function is mine warfare on the high seas.Coastal Defense Type
All ships whose primary function is coastal patrol and interdiction.Mobile Logistics Type
Ships which have the capability to provide direct material support to other deployed units operating far from home base.Auxiliary
Support Ships
Support ships are not designed to participate in combat, and are generally not armed.Support Type
A grouping of ships 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. (Includes smaller auxiliaries which by the nature of their duties, leave inshore waters).Service Type Craft
A grouping of navy-subordinated craft (including non-self-propelled) designed to provide general support to either combatant forces or shore-based establishments.
The USS Constitution, formerly IX 21, was reclassified to none, effective September 1, 1975.