The Västergötland class of diesel-electric submarines was introduced in 1987 by the Swedish Navy. 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 air-independent propulsion system equipped with Stirling engines. They have been recommissioned as the new Södermanland class.
The other two had been put in reserve until November 2005, when they were sold to the Republic of Singapore Navy as the Archer class. They are to be refitted to Södermanland-class standards and receive additional climatisation for use in tropical waters.