Knox class frigates were United States Navy ships, originally laid down as ocean escorts (formerly called destroyer escorts), but were all redesignated as frigates on 30 June 1975 in the USN 1975 ship reclassification and their hull designation changed from DE to FF.
The lead ship of the class was the USS Knox (DE-1052), laid down October 5, 1965 and commissioned April 12, 1969, at Todd Shipyards in Seattle.
These ships were designed primarily as antisubmarine (ASW) platforms. They each had AN/SQS-26 hull-mounted sonar manufactured by General Electric and capable of active echo ranging in the 3.2 kHz range. The active modes of operation included omni-directional, phased directional, bottom bounce, and convergence zone. The battle displays included A and B scans. There was also a "Unit 31" chart readout display capable of long-distance passive detection, often well beyond the ranges capable of the surface search radar. The frigates were also equipped with an AN/AQS-35V Independent Variable Depth Sonar (IVDS) manufactured by EDO Corporation of College Point, NY, operating actively in the 13 kHz range with dual Planned Position Indicator (PPI) battle displays. The IVDS' sonar transducers were packaged within a 2 ton fiberglass-enclosed "fish" containing the sonar array and a gyro-compass/sensor package launched by the massive 13V Hoist from a stern compartment, located just beneath the main deck, to depths of up to 600 feet (180 m). The IVDS could take advantage of water layer temperature conditions in close-range (less than 20,000 yard) submarine detection, tracking and fire-control.
At 4,200 metric tons (4,130 tons), with a length of 438 feet (133.5 metres)and a beam of 47 feet (14.3 m), they are driven by a single screw geared turbine developing 35,000 shaft horsepower (26 MW), giving them a speed of 27 knots (50 km/h). The steam plant for these ships consists of two Babcock & Wilcox "D" type boilers, each equipped with a high-pressure (supercharger) forced draught air supply system, allowing a plant working pressure of 1,200 PSI and 1000 °F superheat. This design allows fast acceleration, crucial while prosecuting a submarine attack. They are equipped with one 5 in (127 mm) 54 calibre Mark 42 gun forward, an ASROC abaft the gun and forward of the bridge. Since they are single purpose platforms their surface defense capability is nominal; however they do mount Harpoon missiles and Mk-46 torpedoes. The aft weapons point was originally outfitted with Mk 25 basic point defense missile systems (BPDMS) for launching Sea Sparrow missiles. These were eventually refitted with a 20 millimetre Phalanx CIWS. They are equipped with a helicopter hangar aft.
These ships were retired with the end of the Cold War and the removal of the need for an advanced ASW capability. By 1994 all ships of this class had been retired from the US Navy, although some remain in service with foreign nations such as Egypt, Taiwan, Thailand, Turkey and Mexico.
