https://en.wikipedia.org/wiki/Gotland-class_submarine https://en.wikipedia.org/wiki/Gotland-class_submarine > The Gotland-class submarines of the Swedish Navy

https://en.wikipedia.org/wiki/Gotland-class_submarine https://en.wikipedia.org/wiki/Gotland-class_submarine > The Gotland-class submarines of the Swedish Navy are modern diesel-electric submarines, which were designed and built by the Kockums shipyard in Sweden. They are the first submarines in the world to feature a Stirling engine air-independent propulsion (AIP) system, which extends their underwater endurance from a few days to weeks. ... > On the water surface, the submarine is powered by two sets of MTU engines. While submerged, the Kockums-built Stirling engine AIP system is used to drive a 75-kilowatt (101 shp) generator for either propulsion or charging the batteries.