The Archer class submarines are the newest class of diesel-electric submarines in active service with the Republic of Singapore Navy (RSN). Originally launched as the Swedish Navy Västergötland class submarines HMS Hälsingland and HMS Västergötland in 1986 and 1987, the two submarines were sold to Singapore in November 2005 and relaunched in June 2009 and October 2010 respectively after extensive modernisation by Kockums, which included a refit to Södermanland class standards, the insertion of a new hull section with an air independent propulsion system, and additional climatisation for use in tropical waters.