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Knox class

Anti-submarine warfare frigate

Knox class

The numerous Knox class were the last steam-powered frigates built for the US Navy

 
 
Country of origin United States
Entered service 1969
Crew 257 men
Sea endurance ~ 60 days
Dimensions and displacement
Length 133.5 m
Beam 14.3 m
Draught 7.6 m
Displacement, standard 3 020 tons
Displacement, full load 4 066 tons
Propulsion and speed
Speed 27 knots
Range 8 300 km at 20 knots
Propulsion 2 x steam boilers and one steam turbine, 35 000 shp, delivering power to 1 shaft
Airwing
Helicopters 1 x SH-2 Seasprite
Armament
Artillery 1 x 127 mm/L54 dual-purpose gun, 1 x Mk.15 Phalanx 20 mm CIWS (on some vessels)
Missiles 1 x 8-cell launcher for a mix of RUR-5 ASROC anti-submarine missiles and Harpoon anti-ship missiles, 1 x 8-cell launcher for RIM-7 Sea Sparrow SAMs (on some vessels)
Torpedoes 4 x 325 mm torpedo tubes

 

   Built during the 1960s and 1970s, the Knox class frigates were at the time of their completion the largest class of fleet warships constructed by the United States since World War 2 (not counting vessels laid-down during the war, and completed afterwards). They also hold the special distinction of being the last US fleet warships with oil-fired boilers, and for a time, they were also the last US destroyer-type vessels with a steel hull, although the Knox class had aluminum superstructures.

   This class was developed in response to unforeseen expenses in the construction of the preceding Brooke class frigates, which resulted in only 6 of 19 planned vessels being built. Rather than building another guided missile frigate armed with the Tartar Surface-to-Air Missile (SAM) system, Secretary of Defense Robert S. MacNamara directed the US Navy to build a class of gun frigates instead, in order to keep the program cost down.

   The resulting design changed little from the Brooke class, but omitted the Tartar launcher and guidance radars. They were at first meant to use the MIM-46 Mauler SAM system instead of the Tartar, as well as a more elaborate lightweight boiler system, but problems with both of these technologies resulted in the same boilers as the Charles F. Adams class destroyers being used instead, and SAM armament being omitted altogether. As with all other US frigates, the new vessels would be propelled by a single screw.

   When the Knox class was authorized, they were classified a destroyer escorts, and received DE-series pennant numbers. Under the US Navy's 1975 ship reclassification, the Knox class were re-rated as "frigates", and received the FF prefix accordingly. However, still retained their destroyer escort pennant numbers through the rest of their ownership by the US Navy.

   The first vessel (FF-1052 Knox) was laid-down on October 5th 1965, and the last in the 46-strong class (FF1097 Moinester) was commissioned on February 11th 1974. FF-1052 though FF-1054, FF-1062, FF-1064, FF-1066, and FF-1071 were built by the Todd shipyard in Seattle, Washington; FF-1055, FF-1058, FF-1060, FF-1067, FF-1071, FF-1074, and FF-1076 were built at the Todd shipyard in San Pedro, California; FF-1057, FF-1063, FF-1065, FF-1069, and FF-1073 were built by the Lockheed shipyard in Seattle, Washington; and FF-1056, FF-1059, FF-1061, FF-1068, FF-1072, FF-1075, and FF-1077 though FF-1097 were all constructed at the Avondale shipyard near Westwego, Louisiana. The decision to have Avondale build most of the later vessels was made as cost-cutting measure. Interestingly, the Lockheed shipyard had also built 3 of the Brooke class frigates, but Bath Iron Works (who built the other 3 Brook class frigates) was not awarded a contract to build any vessels of the Knox class. Ten vessels that were originally planned were later canceled.

   The Knox class initially revealed disappointing seakeeping, with the bow and forecastle tending to be excessively wet in rough seas. From 1980 onwards this was corrected by the addition of a hull knuckle or spray bulwark to each of the vessels (some ships received both). Following the modifications, the class demonstrated satisfactory seakeeping in rough seas.

   The Knox class has essentially the same layout as the Garcia class frigates, with a flared hull, a slightly-raked clipper bow, and a transom stern. The forecastle is occupied by a gun turret and a box-shaped missile launcher; each ship has spray bulwarks on the forecastle, a knuckle on the side of the hull just behind it, or both. The sides of the hull rise up the sides of the fore and aft superstructures, joined by a lower and narrower deckhouse. The forward superstructure is large and low, with a low bridge in front and the ship's mack toward the aft end. The aft section of the superstructure functions mainly as the ship's helicopter hangar, and had hangar doors on its aft end, and numerous small antennae on top. The mack is tall and conical, with a distinctive, dish-like crow's nest, topped with an array of sensor and communications antennae; located in the center of the superstructure, as cell as the center of the ship's length. Atop the after quarterdeck and behind the hangar is a large helipad, with a shallow rhombus shape, and narrower than the rest lf the hull. The aft quarterdeck has the same freeboard as the rest of the hull, with a box-like missile launcher or CIWS turret on the fantail. The underside of the ship (often seen during overhauls in drydock) features a large sonodome, two small trapezoidal stabilizers, small chines, and flat keel, with a single shaft and single, large trapezoidal rudder.

   The sensors and fire controls of the Knox class include an AN/SPS-40 air search radar, an AN/SPS-67 surface search radar, an AN/SQS-26 sonar, an AN/SQR-18 towed array sonar system, a Mk.68 gun fire control system, a Mk.114 Anti-Submarine Warfare (ASW) fire control system, and a Mk.115 missile fire control system; 25 vessels of the class also have a AN/SQS-35 IVDS sonar. The AN/SQS-35 systems were later modified to tow an AN/SQR-18A TACTASS passive towed array sonar. In addition to conventional radios, the Knox class also have an OE-82 satellite navigation system, an SRR-1 satellite communications receiver, and a WSC-3 satellite communications transceiver. The electronic warfare suite includes an AN/SLQ-32 electronics warfare system, a Prairie Masker system, two Mk.36 SRBOC chaff mortar arrays, and an SLQ-25 Nixie towed missile decoy.

   Note that the aforementioned electronics reflect the last configuration of the Knox class in US service. Ships sold abroad may have different or additional electronics.

   The Knox class is steam-powered, with each vessel having two Type D supercharged 1,200-psi boilers. 25 vessels in the class are powered by Combustion Engineering boilers, while the remainder are instead powered by Babcock & Wilcox boilers. All Knox class frigates are powered by a Westinghouse geared steam turbine, driving a single five-blade screw with 35 000 shp. Enough steam is supplied by either boiler to produce enough power for the Knox class to achieve 75% of its designed speed; in fact, they normally only run on one boiler for this reason, and fire the second boiler only when full speed and acceleration are required. As with all US frigates, only one shaft is used to propel the vessel. Total bunkerage is 600 tons of oil, allowing for a maximum range of 8 300 kilometers (4 500 nautical miles) at 20 knots. Although Knox class frigates have at times reached or exceeded 30 knots, they are officially rated for a top speed of 27 knots. A single rudder gives the class a turning circle of about 300 m.

   Curiously, the FF-1052 Badger was able to make 32 knots during sea trials, even though this feat was no designed nor required (nor even expected). This made her the fastest Knox class frigate ever built. A careful inspection of the Badger after the sea trials was unable to determine how she was able to attain such a high speed.

   The main gun of the Knox class is the Mk.42 127 mm/L54 dual-purpose gun, in a single-gun turret. It traverses through +/- 150 degrees at up to 40 degrees per second, and elevates from -15 / +85 degrees at up to 25 degrees per second. The Mk.42 fires a 31.5 kg projectile out to 23 691 m, with an anti-aircraft ceiling of 15 728 m (also, a rocket-assisted projectile for this gun has a range exceeding 30 000 m). This weapon is highly effective against ships, aircraft, and shore targets like, and even some anti-ship missiles.

   The primary ASW weapon of the Knox class is the RUR-5 ASROC anti-submarine missile, which is launched from a Mk.16 8-cell launcher. The launcher can fire this 487 kg missile out to a maximum range of 19 km. The missile breaks-open at a predetermined height from the water, and its warhead continues to the surface via parachute. The warhead used in most models is a complete Mk.46 torpedo, though one model retired in 1989 instead carried a W44 thermonuclear depth charge. An interesting feature of the Mk.16 is that its 8 launch cells are arranged in four separate "stacks" of two, each of which can actually be elevated independently. This launcher is also commonly called the "Matchbox", in reference to its shape.

   The Knox class also launches the Mk.46 torpedo directly. This 324 mm, acoustic homing torpedo has a range of 11 km, a maximum depth of approximately 365 m, and steams at approximately 40 knots. It weighs 230 kg, and carries a warhead containing 43.9 kg of PBXN-103, an insensitive polymer-based explosive compound equal in yield to 1.68 times its weight in TNT. The Mk.46 may also be employed effectively against surface ships, though its very short range makes it far from ideal for that purpose. Helicopters operating from Knox class frigates can also be used to deliver the Mk.46.

   Following an early 1980s refit, all of the Knox class frigates received an additional weapon on their fantail, behind the helipad. On some vessels it was a Mk.29 8-cell missile launcher for the RIM-7 Sea Sparrow SAM, but on the others, it was a Mk.15 Phalanx 20 mm CIWS. Each was a very sparse setup, as no reloads were available for the Sea Sparrow launcher, and the relatively small ammunition capacity of the Phalanx was never expanded.

   There are two decidedly strange attributes of the weapons on the Knox class. Following an early 1980s refit they are outfitted to fire their Harpoon missile from the same Mk.16 launcher normally used for the ASROC missiles. And rather than the usual rotating 3-tube torpedo launchers found on most contemporary Western warships, the Knox class has four fixed tubes built directly into the superstructure.

   The total ammunition load includes 600 127 mm shells, 16 ASROC and/or Harpoons (usually 8 ASROCs and 8 Harpoons), 22 Mk.46 torpedoes, and an unknown quantity of helicopter-served ordnance, plus 989 20 mm shells or 8 Sea Sparrow SAMs.

   The Knox class has an aft helipad, and a hangar with room for one small helicopter. A DASH helicopter drone was originally carried, but it was eventually replaced by the SH-2 Seasprite.

   Initially not well-received by the US Navy's destroyermen (for the class' lighter armament, weaker propulsion, and significantly larger size than the Gearing class destroyers then still in widespread use), the Knox class came to be known in their early years as "MacNamara's Folly". This attitude gradually changed over the years however, as the Knox class proved their worth as rugged and reliable escort vessels. The Navy's leadership was less fond of them however, and Knox class was retired from US service unusually early; none were operational more than 23 years with the US, and many went to the breakers (or to the ocean floor) with decades of longevity left on them.

   All 46 vessels were decommissioned between 1991 and 1994, and all were stricken from the US Navy's list in 1995, excluding several vessels that had already been sold abroad. 9 have been scrapped, 6 have been sunk as targets, and 31 were passed on to foreign navies. Interestingly, despite their long operational service with several different navies through multiple conflicts, the Knox class frigates have never fired a shot in anger.

   Three vessels, the FF-1056 Connole, FF-1068 Vreeland, and FF-1075 Trippe, were transferred to Greece, where they were re-named F456 Iprios, F458 Macedonia, and F457 Thraki. The Iprios and Macedonia were decommissioned in 1999 and 2003, respectively, while the Thraki had only served 2 years with the Hellenic Navy when she was destroyed by an oil fire in 2003 while docked at Crete. The Iprios and Macedonia are in mothballs, while the Thraki has been sunk as a target.

   Turkey is the most numerous buyer, with 12 vessels; the FF-1059 W. S. Sims, FF-1062 Reasoner, FF-1076 Fanning, FF-1079 Bowen, FF-1080 Paul, FF-1082 Elmer Montgomery, FF-1084 McCandless, FF-1085 Donald B. Beary, FF-1090 Ainsworth, FF-1091 Miller, and FF-1092 Thomas C. Hart. In Turkish service, the Reasoner, Bowen, McCandless, Donald B. Beary, Ainsworth, and Thomas C. Hart were renamed the F-252 Kocatepe, F-257 Akdeniz, F-257 Trakya, F-255 Karadeniz, F-256 Ege, and F253 Zafer, respectively. The ex-W. S. Sims, ex-Paul, ex-Elmer Montgomery, and ex-Miller were acquired by Turkey as parts hulks, and were not reactivated. As of 2016, the Trakya, Karadeniz, and Zafer are still in active service, while the Akdeniz was retired in 2011 and is in reserve, and the Ege was made into a museum ship. The Kocatepe was sunk as a target in 2006.

   Mexico purchased 4 vessels, the FF-1062 Whipple, FF-1066 Shields, FF-1067 Francis Hammond, and FF-1094 Pharris, which were renamed the F-211 Ignacio Allende, F-214 Almirante Francisco Javier Mina, F-212 Mariano Abasolo, and F-213 Guadalupe Victoria. As of 2016, all 4 vessels remain in active service with the Mexican Navy.

   Two vessels, the FF-1089 Jesse L. Brown and FF-1097 Moinester were transferred to Egypt in 1998. They were renamed the F.961 Damiyat and F.966 Rasheed. Both are still in active service with the Egyptian Navy.

   Two vessels, the FF-1077 Ouellet and FF-1095 Truett, were purchased by Thailand in 1998 and 1999. Following refits and a service life extensions costing some $14 million each, the Ouellet and Truett were commissioned by the Royal Thai Navy as the FFG-462 Phutthaloetla Naphalai and the FFG-461 Phutthayotfa Chulalok. Both are still in active service.

   Taiwan is the second-largest export customer of the Knox class, having purchased 8 vessels; the FF-1073 Robert E. Peary, FF-1078 Joseph Hewes, FF-1081 Aylwin, FF-1083 Cook, FF-1086 Brewton, FF-1087 Kirk, FF-1088 Barbey, and FF-1096 Valdez. These were reconstructed into a subclass of the Knox, the Chi Yang class, and were recommissioned in the ROCN as the FF-932 Chi Yang, FF-935 Lan Yang, FF-938 Ni Yang, FFG-936 Hai-Yang, FFG-933 Fong Yang, FF-934 Fen Yang, FFG-937 Hwai Yang, and the FF-939 Yi Yang. The Chi Yang and Hai-Yang were decommissioned in 2015 to serve as parts ships, but the other 6 vessels are still in active service.

   Spain built 5 Brooke class frigates based on the Knox class, which were commissioned in the 1970s. However, all of them were decommissioned in the 2000s.

   The surviving Knox class Frigates will likely serve into the 2020s.

 

Related vessels

 

   Garcia class: The preceding class of US frigates, and the design basis of the Knox class. 10 were built most of which were scrapped; two that were sold to Brazil are in reserve.

   Glover (FF-1098): Built as one of the 10 Garcia class frigates, the Glover was refitted with experimental electronics and sensors, and given a unique pumpjet propulsion system instead of a conventional screw. She was decommissioned in 1990, and broken-up for scrap in 1994.

   Brooke class: These were simply Garcia class frigates with a Tartar SAM launcher in place of the second 127 mm gun turret. Six were constructed, though all have since been retired and disposed of.

   Baleares class: Knox class frigates built under license in Spain, with several local modifications. Five were built, which served the Spanish Navy from 1974 to 2008. All have been retired, and are laid-up pending a decision on their final fate. The Baleares class was replaced in service by the Alvaro de Bazan class frigates.

   Chi Yang class: These are former US Navy Knox class frigates, bought by Taiwan and modernized with many new weapons and electronics. A total of 8 were converted, and 7 are still in service with the Taiwanese Navy.

 

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Knox class

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Knox class

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Knox class

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Knox class

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Knox class

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Knox class

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Knox class

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Knox class

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