Sjöormen-class submarine

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R.S.S. Chieftain.jpg
RSS Chieftain
Class overview
Name: Sjöormen class
Preceded by: Draken class
Succeeded by: Näcken class
Planned: 5
Completed: 5
Active: 4
Retired: 1
General characteristics
Type: Submarine
  • Surfaced: 1,075 t (1,058 long tons; 1,185 short tons)
  • Submerged: 1,400 t (1,400 long tons; 1,500 short tons)
Length: 51 m (167 ft 3.9 in)
Beam: 6.1 m (20 ft 0.2 in)
Draught: 5.8 m (19 ft 0.3 in)
  • Surfaced: 15 knots (28 km/h; 17 mph)
  • Submerged: 20 knots (37 km/h; 23 mph)
Endurance: 21 days
Test depth: 150 m (490 ft)
Complement: 23
Sensors and
processing systems:
  • 4 × 533 mm (21 in) torpedo tubes
  • 2 × 400 mm (16 in) torpedo tubes
  • Mines

The Sjöormen class were a group of submarines built for the Swedish Navy in the late 1960s. They had a teardrop hull shape and were capable of diving to 150 metres (490 ft). 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 x-rudder and anechoic tiles.[1] Both speed and underwater endurance was at this time very high for a conventional submarine. The submarines were retired by Sweden in the early 1990s. In the late 1990s, four submarines were acquired by the Republic of Singapore Navy and relaunched as the Challenger class following modernisation and tropicalisation.


As built, the Sjöormen class were designed with a teardrop hull shape, based on the United States' Barbel class. They had bow planes on the sail and their stern diving planes were configured in a x-shape.[2] They had a standard displacement of 1,075 tonnes (1,058 long tons; 1,185 short tons) and 1,400 tonnes (1,400 long tons; 1,500 short tons) when dived.[3][a] The submarines had a waterline length of 50 metres (164.0 ft) and a length overall of 51 metres (167.3 ft). They had a beam of 6.1 metres (20.0 ft) and a draught of 5.8 metres (19.0 ft). The Sjöormen class was powered by a diesel-electric propulsion system composed of two Pielstick diesel engines providing power to a ASEA electric motor driving one shaft with a five-bladed propeller. The entire system was rated at 2,200 brake horsepower (1,600 kW). This gave the submarines a surfaced speed of 15 knots (28 km/h; 17 mph) and 20 knots (37 km/h; 23 mph) submerged. The vessels had an endurance of 21 days and could reach a depth when dived of 150 metres (490 ft). Their diving depth is limited by the shallow waters of the Baltic Sea compared to the ocean depths.[2][3]

As built the Sjöormen class were equipped with suface search radar and sonar.[3] The submarines were armed with four 533 mm (21 in) torpedo tubes located in the bow for surface attack and two 408 mm (16 in) 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.[2][3]

Swedish upgrades[edit]

In 1984–85, the Sjöormen class received upgraded Ericsson IBS-A17 fire control system and CSU-83 sonar suite. In 1992, refits began on Sjölejonet and Sjöhunden that improved their electronics and their towed sonar array.[2]


Ship name Builder Launched Commissioned Status
HSwMS Sjöormen Kockums 25 January 1967 31 July 1968 sold to Singapore as RSS Centurion
HSwMS Sjölejonet Kockums 29 June 1967 16 December 1968 sold to Singapore as RSS Conqueror
HSwMS Sjöbjörnen Karlskrona Navy yard 9 January 1968 28 February 1969 sold to Singapore as RSS Challenger
HSwMS Sjöhunden Kockums 21 March 1968 25 June 1969 sold to Singapore as RSS Chieftain
HSwMS Sjöhästen Karlskrona Navy yard 6 August 1968 15 September 1969 sold to Singapore as spare parts

Service history[edit]

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 Gotland class became operational, but due to lack of funding, were all laid up in 1993.[2]

Singapore service[edit]

Four submarines were sold to the Republic of Singapore Navy in the 1990s and entered service as the Challenger class following modernisation and tropicalisation.[4][5]



  1. ^ Gardiner & Chumbley have the standard displacement as 1,125 tonnes (1,107 long tons; 1,240 short tons).[2]


  1. ^ [1][dead link]
  2. ^ a b c d e f Gardiner & Chumbley, 1995, p. 446.
  3. ^ a b c d Chant 1984, p. 77.
  4. ^ "Dr Tan Launches First Submarine in Sweden". Ministry of Defence Singapore. Retrieved 6 December 2012. 
  5. ^ "Submarine Tropicalisation Programme". MINDEF. Retrieved 6 December 2012. 


  • Chant, Christopher (1984). Naval Forces of the World. Seacaucus, New Jersey: Chartwell Books. ISBN 0-89009-626-0. 
  • Gardiner, Robert; Chumbley, Stephen; Budzbon, Przemysław, eds. (1995). Conway's All the World's Fighting Ships 1947–1995. Annapolis, Maryland: Naval Institute Press. ISBN 1-55750-132-7. 

External links[edit]