The pressure hull had been cut in two after the sail and a 12 m (39 ft 4 in) 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.

As of 2023[update], Södermanland is planned to remain in service until at least 2024-25 when it was to be replaced by the future Blekinge-class submarines.

[3] Two submarines of similar design, known as the Archer class are in service with the Republic of Singapore Navy.