HSwMS Sjöbjörnen (Sbj)

HSwMS Sjöbjörnen (Sbj), Sw. meaning sea bear, was the third ship of the Swedish submarine class Sjöormen, project name A11.

Development
The planning of the class included a number of different AIP solutions including nuclear propulsion. However, the ships where finally completed with for the time extremely large batteries. The ship was a single-hulled submarine, with the hull shape influenced by the American experimental submarine USS Albacore (AGSS-569). The hull was covered with rubber tiles to reduce the acoustic signature (anechoic tiles), at this time a pioneering technology. The Sjöormen-class submarine also pioneered the use of an x-shaped (as opposed to cross-shaped) rudder as a standard (as opposed to experimental) feature.

Service in Sweden
The submarine served in the Swedish Navy for almost 30 years and was then sold to Singapore in 1997 together with its four sister ships.

Service in Singapore
HSwMS Sjöbjörnen was renamed RSS Challenger and Singapore reacquired the boat on 28 May 1999. She was commissioned on 26 June 2004 after a major refit. After 11 years in the Republic of Singapore Navy, she was decommissioned on 11 March 2015 and scrapped.