Ratanakosin-class corvette

The Ratanakosin-class corvettes (รัตนโกสินทร์) are a class of two corvettes that were built for the Royal Thai Navy in the 1980s. Constructed by Tacoma Boatbuilding Company in the United States, a third was planned to be built in Thailand but was canceled before construction could begin. The Ratanakosin class is used as flagships for squadrons of fast attack craft.

One of the two, HTMS Sukhothai, sank in a storm on 18 December 2022.

Design
The Ratanakosin class is based on the Saudi Arabian Badr-class corvette design. They have a normal displacement of 840 t and 960 t full load. The corvettes measure 76.82 m long with a beam of 9.55 m and a draft of 2.44 m. The class is powered by MTU 20V1163 TB83 diesel engines, each driving one shaft rated at 16000 bhp. This gives the vessels a maximum speed of 26 kn and a range of 3000 nmi at 16 kn. The ships have a complement of 15 officers and 72 enlisted.

The class is equipped with one Decca 1226 and one HSA ZW-06 surface-search radar, one HSA DA-05 air/surface-search radar, one HSA WM-25 fire-control radar, one HSA LIROD-8 optical fire-control system, and one STN Atlas DSQS-21C hull-mounted sonar. The corvettes are armed with two quad launchers for eight RGM-84 Harpoon anti-ship missiles and one octuple Albatros launcher for 24 Selenia Aspide surface-to-air missiles (SAM). Furthermore, the vessels are armed with one Otobreda 76 mm gun, two Bofors 40 mm guns in a twin Otobreda mount, and two 20 mm Oerlikon GAM-B01 cannons. The Ratanakosin class is also equipped with two Mark 32 triple torpedo tubes for Sting Ray torpedoes.

Construction and career
The Royal Thai Navy ordered two corvettes from Tacoma Boatbuilding Company in Tacoma, Washington, United States on 9 May 1983. The lead ship was laid down on 6 February 1984. Named Ratanakosin, the vessel was launched on 11 March 1986. The second ship in the class was laid down on 26 March 1984. Named Sukhothai, the vessel was launched on 20 July 1986. Ratanakosin was commissioned on 26 September 1986 and Sukhothai on 19 February 1987. The third ship, which was planned for construction in Thailand, was canceled before construction began. This was due to increased interest by the Royal Thai Navy in Vosper Thornycroft's design that became the Khamronsin-class corvette. Ratanakosin-class corvettes are used as flagships for squadrons of fast attack craft.

Sukhothai sank in a storm on 18 December 2022.