Frigate
In modern military terminology, a frigate is a warship intended to protect other warships and merchant ships as anti-submarine warfare (ASW) combatants for amphibious expeditionary forces, underway replenishment groups, and merchant convoys.
Sailing frigate and its rigging.
During the age of sail, a frigate was a sailing vessel designed for speed, with a flush gun deck carrying 24 to 44 guns, used as scouts attached to larger fleets, as commerce raiders, for blockade duty, and for the protection of convoys. With the introduction of steam and steel warships frigates as a class of warship passed out of use until World War II when they were reintroduced by the British as an antisubmarine escort vessel larger than a corvette but smaller than a destroyer. Sail frigates and steam frigates evolved into cruisers; they are only related to modern frigates by name.
The oldest commissioned warship in the US Navy is the USS Constitution, better known as "Old Ironsides," a frigate put into service in the 1790s. It is the oldest commissioned warship afloat in the world; the HMS Victory, though older, is maintained in drydock.
In the United States Navy, guided missile frigates (with the FFG hull classification symbol) bring an anti-air warfare (AAW) capability to the frigate mission, but they have some limitations. Designed as cost-efficient surface combatants, they lack the multi-mission capability necessary for modern surface combatants faced with multiple, high-technology threats and offer limited capacity for growth.
In an attempt to overcome these limits and provide escorts that could free the nuclear carrier battle groups from dependence on oilers, the US Navy commissioned several "frigates" (which were actually cruisers built on destroyer-style hulls), some of which (Bainbridge, Truxtun, and the California and Virginia classes) were nuclear, in the 1960s. They were far larger than any other frigates ever seen, and all except the Farragut class (which were smaller than the others) were properly reclassified as cruisers in 1975 and struck from the Naval Vessel Register in the 1990s. USS Long Beach (CGN-9, ex-CGN-160, ex-CLGNGN-160) was the last cruiser in the United States Navy to be laid down on a cruiser-style hull.
The US Navy altered the designation of the DE (ocean escort) and DEG (ocean escort, guided missile) in June, 1975. The new nomenclature was FF (frigate) and FFG (frigate, guided missile).
Frigates of the United States
Mississippi was redesignated a CGN before launch and Arkansas was designated a CGN before being laid down; neither served as frigates in the US Navy.
The US Navy intends to replace all existing frigates with the Littoral Combat Ship, of which as many as 60 may be built.
See also
Partially from: http://www.chinfo.navy.mil/navpalib/factfile/ships/ship-ffg.html