The submarine design combined the best properties from the and the . Submarines of the Västergötland class had greater submarine hunting capacity than previous classes, partly due to the fact that they were equipped with a new modern submarine torpedo. The submarines in the Västergötland class were able to fire up to six heavy and six light wire-guided torpedoes at the same time against different targets.[1]
The Västergötland class included the submarines HSwMS Södermanland and . After significant upgrades, these two submarines were reclassified to a new .
Between 2000 and 2004, Södermanland and Östergötland underwent extensive modifications, were extended by and fitted with air-independent Stirling engines. At the same time, the submarines would be modified to handle international missions with operations in hot and salty waters. The conversion of the two submarines became so extensive that Kockums decided to reclassify the submarines to a new Södermanland class.[2]
During 2022, Södermanland underwent yet another life extension program, in order to be operational until 2028.[3]
As Östergötland was decommissioned in 2021, Södermanland is the only remaining submarine in its class.