A11 Sjöormen (Sea Serpent)

The Sjöormen (Type A 11) (Sea Serpent)-class submarines were designed in the early 1960s by Kockums, Malmö. Three were built by them with a further two by Karlskronavarvet, Karlskrona. Launched in 1967 and 1968, the five boats: Sjöormen, Sjolejonet, Sjöhunden, Sjöbjörnen and Sjöhästen entered service with the Royal Swedish Navy (RSwN) between July 1968 and June 1969. They were optimised for the RSwN's ASW operations and emphasised underwater manoeuvrability over diving depth, allowing them to out-turn most of the Warsaw Pact ASW escorts encountered in the Baltic, as well as most of the NATO escorts. All five boats were withdrawn from service with the RSwN.

In September 1995 it was announced that Republic of Singapore Navy (RSN) would acquire one of these submarines for training purposes only. The RSN subsequently acquired Sjöbjörnen and another three submarines of the class under the Riken Project between 1995 and 1997 to develop a subsurface operations capability and experience (Riken being the original RSN name of the first boat, Challenger). Conqueror (ex-Sjölejonet) was recommissioned in Singapore on 24 July 2000 and Chieftain (ex-Sjohunden) on 24 August 2002. Challenger (ex-Sjöbjörnen) and Centurion (ex-Sjöormen) remained in Sweden to support training until January 2004 when they were transported to Singapore. Ex-Sjohasten was also shipped as a source of spares. Centurion was recommissioned on 26 June 2004. The program was managed by the Singapore Defence Science and Technology Agency (DSTA). The four operational boats were modernised by Kockums at Karlskrona for service in warm waters.

Main characteristics: Displacement 1495 tonnes Length overall 60,5 m Diameter of the hull 6,1 m Weaponry 4 tubes for heavy torpedos type 613, 62 2 tubes for torpedos type 43, 45 Crew 25