|Operators:||Republic of Singapore Navy|
|Succeeded by:||Archer class|
|Length:||50 m (164 ft 1 in)|
|Beam:||6.1 m (20 ft 0 in)|
|Draught:||5.1 m (16 ft 9 in)|
In 1995, the RSN acquired a Challenger class (formerly known as Sjöormen class) submarine from the Swedish Navy and another three in 1997, making them Singapore's first underwater platforms. It is believed that the Challenger class were purchased to develop the required submarine operations expertise before selecting a modern class of submarines to replace them, since all the boats are over 40 years old.
|RSS Challenger (ex-HMS Sjöbjörnen)||26 September 1997||retired 11 March, 2015|
|RSS Conqueror (ex-HMS Sjölejonet)||28 May 1999||22 July 2001||in active service, as of 2011|
|RSS Centurion (ex-HMS Sjöormen)||28 May 1999||26 June 2004||retired 11 March, 2015|
|RSS Chieftain (ex-HMS Sjöhunden)||22 May 2001||24 August 2002||in active service, as of 2011|
The Challenger class submarines have undergone the Riken modernisation programme tailored to the specific operational conditions of the Singapore Navy. As the submarines were designed by the Swedish for operations in the Baltic Sea, various modifications were required to suit them to tropical waters. A comprehensive tropicalisation programme was carried out for all four submarines, which involved installing air conditioning, marine growth protection systems and corrosion-resistant piping.
- "Dr Tan Launches First Submarine in Sweden". Ministry of Defence Singapore. Retrieved 2012-12-06.
- Kaplan, George. "The Republic of Singapore Navy". Navy League of Australia. Retrieved 2012-12-06.
- "The RSN Launches Her Fourth Submarine, the RSS Chieftain". Ministry of Defence Singapore. Retrieved 2011-12-04.
- "Commissioning of RSS Centurion". Ministry of Defence Singapore. Retrieved 2011-12-04.
- "Dr Tony Tan Commissions RSN’s Second Submarine". Ministry of Defence Singapore. Retrieved 2011-12-04.
- "Submarine Tropicalisation Programme". MINDEF. Retrieved 2012-12-06.
- Conway's All the World's Fighting Ships 1947-1995