The Sjöormen class (Sea serpent) was a class of submarines built for the Swedish Navy in the late 1960s. They had a teardrop hull shape and were capable of diving to . At the time of their deployment they were regarded as one of the most advanced non-nuclear submarine classes in the world, incorporating many new features including an x-rudder and anechoic tiles. Both speed and underwater endurance were at the time very high for a conventional submarine. The submarines were retired by Sweden in the early 1990s. In the late 1990s, all five submarines were acquired by the Republic of Singapore Navy (RSN) and four were relaunched as the following modernisation and tropicalisation. The fifth was never relaunched as it was used for spare parts and subsequently scrapped in the 2000s. As of November 2024, the Challenger class has been decommissioned.

Description As built, the Sjöormen class were designed with a teardrop hull shape, based on the United States' . They had bow planes on the sail and their stern diving planes were configured in a x-shape. They had a standard displacement of and when dived. The submarines had a waterline length of and a length overall of . They had a beam of and a draught of . The Sjöormen class was powered by a diesel-electric propulsion system composed of two Pielstick diesel engines providing power to an ASEA electric motor driving one shaft with a five-bladed propeller. The entire system was rated at . This gave the submarines a surfaced speed of and submerged. Designed for the confined waters of the Baltic Sea, the vessels had an endurance of 21 days and a test depth of .

As built the Sjöormen class were equipped with surface search radar and sonar. The submarines were armed with four torpedo tubes located in the bow for surface attack and two torpedo tubes in the stern for either anti-submarine warfare or for naval mines. The Sjöormen class had a complement of 23 officers and enlisted.

Swedish upgrades In 1984–85, the Sjöormen class received upgraded Ericsson IBS-A17 fire control systems and CSU-83 sonar suites. In 1992, refits began on Sjölejonet and Sjöhunden that improved their electronics and their towed sonar array.

Ships Ship nameBuilderLaunchedCommissionedStatusKockums25 January 196731 July 1968sold to Singapore, recommissioned as Kockums29 June 196716 December 1968sold to Singapore, recommissioned as Karlskrona Navy yard9 January 196828 February 1969sold to Singapore, recommissioned as Kockums21 March 196825 June 1969sold to Singapore, recommissioned as Karlskrona Navy yard6 August 196815 September 1969sold to Singapore, not recommissioned, used for spare parts

Service history The Sjöormen class were ordered by the Swedish Navy in 1961. The first boat in the class, Sjöormen, entered service in 1968. In 1992, two vessels in the class, Sjölejonet and Sjöhunden, underwent modernisation. The remaining three were supposed to remain in service until the became operational, but due to lack of funding, all were laid up in 1993.

All five submarines were sold to the Republic of Singapore Navy (RSN) in the late 1990s and four entered service as the following modernisation and tropicalisation, while the fifth was used for spare parts and subsequently scrapped in the late 2000s.

See also Equivalent submarines of the same era

Type 035 Potvis class

References Notes

Citations

Bibliography

External links Official Kockums website on the Challenger-class submarines Covert Shores