Thonburi-class coastal defence ship

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HTMS Thonburi in Yokohama.jpg
HTMS Thonburi
Class overview
Builders: Kawasaki
Operators:Naval Ensign of Thailand.svg  Royal Thai Navy
Preceded by: Ratanakosidra class
Built: 1936–1938
In commission: 1938-1951
Completed: 2
Lost: 2
General characteristics [1]
Type: Coastal defence ship
Displacement: 2,265 long tons (2,301  t)
Length: 76.50 m (251 ft 0 in)
Beam: 14.43 m (47 ft 4 in)
Draught: 4.17 m (13 ft 8 in)
  • MAN diesels, 2 shafts
  • 3,900 kW (5,200 bhp)
Speed: 15.5  kn (17.8 mph; 28.7 km/h)
Complement: 155
  • Belt: 2 12 in (64 mm)
  • Turrets:4 in (100 mm)
  • Barbettes:4 in
  • Decks:1 12–1 in (38–25 mm)

The Thonburi class was a class of coastal defence ships of the Royal Thai Navy. It consisted of two ships built by Kawasaki and delivered in 1938, HTMS Thonburi and HTMS Sri Ayudhya.



Thonburi and her sister ship, Sri Ayudhya, were designed following the incorporation of the earlier Rattanakosindra-class gunboats into the Siamese Navy in the 1920s. The Ratanakosindra class were British-built ships which featured six-inch guns in two turrets and light armor. Under Plaek Pibulsonggram's command, the Siamese Navy began a series of modernization efforts. Priorities for the navy consisted of protecting the extensive Thai coastline, and coastal gunboats were viewed as the best resource. Several foreign firms from European countries offered a variety of designs, but in the end the Japanese company Kawasaki won the tender.

The new vessels were basically larger versions of the earlier Ratanakosindra ships. The ships were laid down at Kawasaki's facilities in 1936, and the first, Sri Ayuthia, was launched on 21 July 1937. The resulting "battleships," as they were referred to in Siam at the time, displaced 2,265 tons, featured increased armor protection (protecting machinery and gun turrets), and were powered by twin diesels produced by MAN of Germany.


Armament consisted of four 8-inch (203 mm)/50 calibre guns mounted in pairs in two turrets. The Japanese 8-inch rifles were of the same type as mounted in early Imperial Japanese Navy heavy cruisers and the aircraft carriers Akagi and Kaga. The main armament had a maximum range of 24,000 metres (26,000 yd) at 25 degrees of elevation. A tower above the bridge featured a gun director for aiming the main guns. Additional armament consisted of four 3-inch and four 40-mm guns.

Public opinion

The new ships were enthusiastically received by the Siamese Navy. Purchasing further vessels of the type was considered by the government, but ultimately it was decided to purchase two Italian-built cruisers in 1938. Both ships were seized by Italy in 1941 before construction had finished, leaving Thonburi and her sister ship as the most powerful combatants in Siamese service.


Ships in class

Ship nameCommissionedDecommissionedStruckFate
Thonburi 31 January 193826 September 194119 June 1959Severely damaged in the Battle of Koh Chang, 17 January 1941; Refitted and became training ship until being struck.
Sri Ayudhya 19 July 1938n/a8 October 1959Sunk during the Manhattan Rebellion, 1 July 1951.

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  1. Gardiner and Chesneau 1980, p. 410.