Lead ship of the class, HTMS Phutthayotfa Chulalok in 2005
Class overview
Builders	Avondale Shipyards, Westwego, Louisiana
Operators	United States Navy ex-Knox-class frigate  Royal Thai Navy
Preceded by	Chao Phraya class
Succeeded by	Naresuan class
Built	1969–1974
In commission	1994–2017
Retired	2
Preserved	1
General characteristics
Type	Frigate
Displacement	4,065 long tons (4,130 t) (standard) 4,260 long tons (4,328 t) (full load)
Length	438 ft (134 m) loa 415 ft (126 m) wl
Beam	46 ft 9 in (14.25 m)
Draft	24 ft 9 in (7.54 m)
Installed power	2 × 1,200 psi (8,300 kPa) boilers 35,000 shp (26,099 kW)
Propulsion	1 × geared steam turbine 1 × shaft
Speed	27 kn (50 km/h; 31 mph)
Complement	250 officers and enlisted
Sensors and processing systems	SPS-40B 2-D air search radar SPG-53 fire control radar SQS-26CX bow sonar SQR-18 towed sonar SLQ-32(V)1 passive intercept
Armament	1 × 5"/54 caliber Mark 45 gun 1 × 20 mm Phalanx CIWS 8 × ASROC anti-submarine missiles 4 × Harpoon missiles 4 × Mk.32 torpedo tubes with Mark 44 torpedoes
Aviation facilities	Helicopter deck and hangar

The Phutthayotfa Chulalok-class frigates are two of forty-six Knox-class frigates originally laid down for the United States Navy 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 Thai Navy acquired them between 1994 and 1996.

The Phutthayotfa Chulalok class are 438 ft (134 m) long overall and 415 ft (126 m) at the waterline, with a beam of 46 ft 9 in (14.25 m) and a draft of 24 ft 9 in (7.54 m), at a standard displacement of 4,065 long tons (4,130 t) and 4,260 long tons (4,328 t) at full load. The steam plant for these ships consists of two Combustion Engineering boilers each equipped with a high-pressure (supercharger) forced draught air supply system, with a plant working pressure of 1,200 psi (8,300 kPa) and 1,000 °F (538 °C) superheat and rated at 35,000 shaft horsepower (26,000 kW) driving a Westinghouse geared turbine connected to a single screw. This gives them a speed of 27 kn (50 km/h; 31 mph).^[1][2]

As built, they were equipped with one 5-inch (127 mm)/54 caliber Mark 42 gun forward, an eight-round ASROC launcher (with 16 missiles carried) abaft the gun and forward of the bridge, with four fixed 12.75 in (324 mm) Mark 32 anti-submarine torpedo tubes. A helicopter deck and hangar for operating the DASH drone helicopter was fitted aft.^[3][4] The helicopter facilities were expanded in the 1970s to accommodate the larger, crewed Kaman SH-2D Seasprite LAMP helicopter.^[5]

USS Ouellet and USS Truett were purchased by Thailand in 1996 and 1999. Thailand had initially leased Truett in 1994. Following refits and a service life extensions costing some $14 million each, Ouellet and Truett were commissioned by the Royal Thai Navy as Phutthaloetla Naphalai (FFG-462) and Phutthayotfa Chulalok (FFG-461). Both are still in active service.^[6][1][2]

In 2013, it was reported that the ships of this class would be retired, Phutthayotfa Chulalok in 2015, and Phutthaloetla Naphalai in 2017.^[7]

Phutthayotfa Chulalok (Thai: พุทธยอดฟ้าจุฬาโลก). The ship is named after the first king of the Chakri Dynasty, King Phutthayotfa Chulaok the Great.

The Royal Thai Navy first leased the ship from the US Navy after she was decommissioned on 30 July 1994. The ship was eventually purchased on 9 December 1999.

Phutthaloetla Naphalai (Thai: พุทธเลิศหล้านภาลัย). The ship is named after the second king of the Chakri Dynasty, King Phutthaloetla Naphalai

The Royal Thai Navy purchased the ship from the US Navy after she was decommissioned on 6 August 1993. The ship subsequently underwent a US $14M refit at the Cascade General Shipyard, Portland, Oregon, and arrived in Thailand in 1998.^[8]

• Friedman, Norman (1997). The Naval Institute Guide to World Naval Weapon Systems 1997–1998. Annapolis, Maryland: Naval Institute Press. ISBN 1-55750-268-4.
• Prézelin, Bernard; Baker III, A.D., eds. (1990). The Naval Institute Guide to Combat Fleets of the World 1990/91:Their Ships, Aircraft and Armament. Annapolis, Maryland: Naval Institute Press. ISBN 0-87021-250-8.

Photo gallery of USS Truett (DE 1095) at NavSource Naval History Photo gallery of USS Ouellet (DE 1077) at NavSource Naval History