The Näcken-class submarines, also known as the A14 type, were built for the Swedish Navy in the late 1970s.

The boats had a teardrop hull and diving depth was 150 metres (490 ft).

Between 1987 and 1988, Näcken and her sister ships were cut in half and an 8-metre (26 ft) long hull section containing a prototype Air-independent propulsion (AIP) using a closed cycle Stirling engine was installed between the aft battery/propulsion & power control room and the engine/motor room.

This technology increased underwater endurance to 14 days and has been adopted in subsequent Swedish submarines.

HSwMS Näcken was temporary leased to the Royal Danish Navy but was returned in 2005.