Södermanland-class submarine

The Swedish Södermanland class of diesel-electric submarines consists of HSWMS Södermanland (Söd) and HSWMS Östergötland (Ögd). These two submarines were originally launched as Västergötland-class submarines in 1987 and 1990, and were relaunched as a new class after extensive modernization in 2003 and 2004 by Kockums AB. The pressure hull had been cut in two after the sail and a 12 m long new section with an air-independent propulsion system was inserted. It contains two Stirling engines which are coupled to electric generators and heated by burning diesel fuel with liquid oxygen stored in cryogenic tanks. The AIP system can provide electric energy to extend the submarine's submerged time from days to weeks.

, Södermanland is planned to remain in service until at least 2024-25 when it was to be replaced by the future Blekinge-class submarines. However, the Östergötland was decommissioned in 2021, and is in material reserve.

Two submarines of similar design, known as the Archer-class submarine are in service with the Republic of Singapore Navy.