The Archer class submarines is an upgrade of Västergötland Class diesel-electric submarines which were originally developed for the Swedish Navy. The modernised submarines are in 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.
The Archer class submarines were designed and built by Kockums AB as single-hull, double compartment submarines optimised to reduce noise and magnetic signature. The two pressure-tight compartments also enhance safety and survivability of the crew. The submarines were designed to operate in the shallow waters of the Baltic Sea and are therefore also optimised for operation in Singapore waters, which have similar depth profiles. The hull integrates a fully equipped eight metre-long Stirling AIP section. The submarines also feature two pressure-tight compartments for increased safety and survivability of the crew. The stealth capabilities were refined for avoiding detection by hostile forces. The submarine has a length of 60.5m, beam of 6.1m and a height of 11.8m. The draught is 5.6m. Archer has a submerged displacement of 1,500t. It can accommodate 28 crew members.
The Command, Control, Computer, Communication and Intelligence (C4I) systems of the Archer Class vessels were modernised to cope with the present and future requirements of the RSN. The advanced sonar system allows the submarines to detect contacts at a further distance, while the torpedo system has a better target acquisition capability, which allows the submarines to engage contacts at a longer range. The Archer Class submarines are armed with six 533mm (21″) and three 400mm (16″) torpedo tubes. The 533mm tubes can launch heavy-weight anti-ship torpedoes, while the 400mm tubes are capable of launching lightweight anti-submarine torpedoes. The onboard torpedo system provides the ability to engage targets at long ranges.
The Archer class submarines are also equipped with Stirling AIP engines. This enables the submarines to have longer submerged endurance and lower noise signature, enhancing the stealth capability of the submarines.The Stirling AIP system substantially raises the sub-merged endurance of submarines. It will act as an alternative to the batteries requiring frequent recharge with the diesel generators. The AIP engines use liquid oxygen (LOX) and diesel fuel. The AIP system complements the diesel-electric engines. The AIP system offers vibration-free and silent operation, while extending the submerged endurance from days to weeks. The propulsion system provides a surfaced speed of 8kt and submerged speed of 15kt.