The Västergötland class of diesel-electric

Diesel-electric

Diesel-electric transmission or diesel-electric powertrain is used by a number of vehicle and ship types for providing locomotion.A diesel-electric transmission system includes a diesel engine connected to an electrical generator, creating electricity that powers electric traction motors...

 submarine

Submarine

A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

s was introduced in 1987 by the Swedish Navy

Swedish Navy

The Royal Swedish Navy is the naval branch of the Swedish Armed Forces. It is composed of surface and submarine naval units – the Fleet – as well as marine units, the so-called Amphibious Corps .In Swedish, vessels of the Swedish Navy are given the prefix "HMS," short for Hans/Hennes...

. The original four ships of her class, HMS Västergötland, HMS Hälsingland, HMS Södermanland and HMS Östergötland, were built between 1983 and 1988 by Kockums AB. The latter two have undergone comprehensive refits, including the insertion of a new hull section with an AIP

Air-independent propulsion

Air-independent propulsion is a term that encompasses technologies which allow a submarine to operate without the need to surface or use a snorkel to access atmospheric oxygen. The term usually excludes the use of nuclear power, and describes augmenting or replacing the diesel-electric propulsion...

 system equipped with Stirling engine

Stirling engine

A Stirling engine is a heat engine operating by cyclic compression and expansion of air or other gas, the working fluid, at different temperature levels such that there is a net conversion of heat energy to mechanical work....

s. They have been recommissioned as the new Södermanland class

Södermanland class submarine

The Swedish Södermanland class of diesel-electric submarines consist of the HMS Södermanland and HMS Östergötland. These two submarines were originally launched as Västergötland class submarines in 1987 and 1990, and have been relaunched as a new class after extensive modernization 2003 and 2004 by...

.

The other two had been put in reserve until November 2005, when they were sold to the Republic of Singapore Navy

Republic of Singapore Navy

The Republic of Singapore Navy is the naval component of the Singapore Armed Forces , responsible for the defence of Singapore against sea-borne threats and protection of its sea lines of communications. Operating within the crowded littoral waters of the Singapore Strait, the RSN is regarded as...

. They are to be refitted to Södermanland-class standards and receive additional climatisation for use in tropical waters.

Units

Ship name	Laid down	Launched	Commissioned	Service	Status
HMS Västergötland		19 July 1986	27 November 1987	1st Submarine flotilla	Sold to Republic of Singapore Navy Republic of Singapore Navy The Republic of Singapore Navy is the naval component of the Singapore Armed Forces , responsible for the defence of Singapore against sea-borne threats and protection of its sea lines of communications. Operating within the crowded littoral waters of the Singapore Strait, the RSN is regarded as...  2005 (deal finished 2008).
HMS Helsingland	1 January 1984	31 August 1987	20 October 1988	1st Submarine flotilla	Sold to Republic of Singapore Navy Republic of Singapore Navy The Republic of Singapore Navy is the naval component of the Singapore Armed Forces , responsible for the defence of Singapore against sea-borne threats and protection of its sea lines of communications. Operating within the crowded littoral waters of the Singapore Strait, the RSN is regarded as...  2005 (deal finished 2008).
HMS Södermanland		12 April 1988	21 April 1989	1st Submarine flotilla	Refitted 2003-2004 to Södermanland class Södermanland class submarine The Swedish Södermanland class of diesel-electric submarines consist of the HMS Södermanland and HMS Östergötland. These two submarines were originally launched as Västergötland class submarines in 1987 and 1990, and have been relaunched as a new class after extensive modernization 2003 and 2004 by... , active.
HMS Östergötland		9 December 1988		1st Submarine flotilla	Refitted 2003-2004 to Södermanland class Södermanland class submarine The Swedish Södermanland class of diesel-electric submarines consist of the HMS Södermanland and HMS Östergötland. These two submarines were originally launched as Västergötland class submarines in 1987 and 1990, and have been relaunched as a new class after extensive modernization 2003 and 2004 by... , active.