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

However, the ships where finally completed with for the time extremely large batteries.

[2] 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.

HSwMS Sjöbjörnen was renamed RSS Challenger after Singapore acquired the boat on 28 May 1999.

After 11 years in the Republic of Singapore Navy, she was decommissioned on 11 March 2015 and scrapped.