Södermanland-Class Submarine

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 (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.

HSwMS Södermanland at sea
Class overview
Name	Södermanland class
Builders	Kockums
Operators	Swedish Navy
Preceded by	Näcken class
Succeeded by	Gotland class
In commission	1989–present
Planned	4
Completed	2
Cancelled	2
Active	1
Retired	1
General characteristics
Displacement	Submerged: 1,500 t (1,500 long tons; 1,700 short tons)
Length	60.5 m (198 ft 6 in)
Beam	6.1 m (20 ft 0 in)
Draft	5.6 m (18 ft 4 in)
Propulsion	2 × Hedemora Diesel-electric engines 2 × Kockums v4-275R Stirling AIP units
Speed	Submerged: 20 kn (37 km/h; 23 mph)
Complement	24
Sensors and processing systems	FAS
Armament	6 × 533 mm (21.0 in) torpedo tubes 3 × 400 mm (15.7 in) torpedo tubes Mines

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. However, the Östergötland was decommissioned in 2021, and is in material reserve.

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