The 46 Knox-class frigates were the largest, last, and most numerous of the US Navy's second-generation anti-submarine warfare (ASW) escorts. Originally laid down as ocean escorts (formerly called destroyer escorts), they were all redesignated as frigates on 30 June 1975, in the 1975 ship reclassification plan and their hull designation changed from 'DE' to 'FF'. The Knox class was the Navy's last destroyer-type design with a steam turbine powerplant.
Due to their unequal comparison to destroyers then in service (larger size with lower speed and only a single screw and 5-inch gun), they became known to a generation of destroyermen as "McNamara's Folly."
These ships were retired from the US Navy at the end of the Cold War due to their relatively high running costs, a declining defense budget, and the need for ships with a more advanced anti-submarine capability. None of the ships served more than 23 years in the US Navy, and by 1994, all of the class had been retired, although some remain in service with foreign nations such as Egypt, Taiwan, Thailand, and Mexico.
Design
Designated SCB No. 199C, the Knox was planned as the follow-on to the twin 5" gun-armed Garcia class frigates and the Tartar missile-equipped s. Their initial design incorporated the prior classes' pressure-fired boilers in a similar-sized hull designed around the massive bow-mounted AN/SQS-26 sonar, with increased endurance and reduced crew size. Anti-submarine armament was to consist of RUR-5 ASROC anti submarine missiles together with the QH-50 DASH drone helicopter, while defensive armament was to be the RIM-46 Sea Mauler short range anti-aircraft missile backed up by a single 5-inch/54 caliber Mark 42 gun.
The design soon ran into problems however, with the US Navy deciding to switch to conventional boilers, requiring a redesign, and the ships became longer and heavier in order to accommodate the less compact power plants. Furthermore, Sea Mauler was cancelled in 1965, leaving the ships to complete without any anti-aircraft system except the 5" gun.
The steam plant for these ships consists of two Combustion Engineering or Babcock & Wilcox "D" type boilers, each equipped with a high-pressure (supercharger) forced draught air supply system, with a plant working pressure of and superheat and rated at driving a single screw. This gives them a speed of .
The ships were designed primarily as anti-submarine warfare (ASW) platforms. Their main anti-submarine sensor was the large bow-mounted AN/SQS-26CX low-frequency scanning sonar, operating as an active sonar at a frequency of about 3.5 kHz and passively at 1.5–4 kHz. The active modes of operation included direct path, to a range of about , bottom bounce, and convergence zone, which could give ranges of up to about , well outside the capability of ASROC, and requiring the use of a helicopter to exploit. An eight-round ASROC launcher (with 16 missiles carried) was fitted between the gun turret and the bridge, backed up by four fixed Mark 32 anti-submarine torpedo tubes. A flight deck and hangar for operating the DASH drone helicopter was fitted aft.
Construction
Ten ships were authorized in Fiscal Year 1964, sixteen in 1965, and ten each for FYs 1966, 67 and 68; six were canceled in 1968, and four more in 1969. While the FY64 and FY65 ships were ordered from four different shipyards, later ships (DE-1078 onwards) were all ordered from Avondale Shipyards in order to cut costs. These ships were built on a production line, with prefabricated modules being assembled upside down, welded together and then rotated into an upright position. They were originally commissioned as destroyer escorts (DEs) 1052–1097 in 1969–1974, but were redesignated as frigates (FF) on 30 June 1975.
The lead ship of the class, , was laid down 5 October 1965, and commissioned 12 April 1969, at the Todd Shipyards in Seattle, Washington.
Modifications
The and subsequent ships of the class were modified to enable them to serve as flagships. The primary change was a slightly different arrangement of the "Officer's Country" staterooms with additional staterooms in a new 01 level structure which replaced the open deck between the boats. The stateroom on the port side under the bridge was designated as a "flag" stateroom, with additional staterooms for flag staff when serving as a flagship. These ships have been referred to as the Joseph Hewes-sub-class .