A Frigate of the modern type are radar- and sonar-equipped antisubmarine and air-defence ships first developed during World War II and still in use today. A Sailing Frigate of the 17th–19th century were types of small and fast warships, usually either the square-rigged sailing ships.
Since the passing of the sailing navy, the word "frigate" has seen rather uncertain usage in the U. S. Navy. After a long hiatus, it was revived in World War II as the "patrol frigate," an escort vessel somewhat more capable than a patrol vessel (or "corvette") but less so than the "destroyer escort," itself a wartime "economy model" destroyer. Right after the war, there was designed a class of "super destroyers" or "destroyer leaders" that were styled "frigates," the "patrol frigates" having been discarded. Because later classes of this type grew into the size range of what had been cruisers, such "frigates" were so reclassified in 1975. At the same time, the lowly "destroyer escorts," of new design and construction but still remembered as "second rate destroyers," were glorified with the name "frigate." And so, when we speak of modern frigates today we most often mean that type of small warship primarily designed to escort convoys and fight submarines or air defence capabilities: definitely not in the same league as the frigates of old.