Stockholm - class corvette " Stockholm " class corvette is a corvette class in the Swedish Navy . Built in Karlskrona 1984 – 1985 , it is armed with eight RBS15 anti - ship missiles , torpedoes , one 57mm cannon and several machine gun s . In 1999 / 2000 the two units in the class were upgraded in the Karlskrona shipyard Kockums . The upgrade included new engines , sensors , stealth technology , and navigation systems , the goal being to bring the technology up to the same level as the " Visby " class . History . The " Stockholm " Class Corvette started as a study for a ship with increased endurance , a project called " Ytattack - 81 " ( Surface combatant - 81 ) , which was built on the torpedo boats of Spica and Spica II class , but with an increased displacement from 230 tons to 350 tons . The engine was to be a CODAG - concept , two diesels and one gas turbine . However , the class looked to become just another desktop project . In the early 1980s a series of submarine incidents occurred within Swedish territorial waters , the most famous of which was U 137 which ran aground outside Karlskrona 1981 . These incidents showed that the Swedish Navy was seriously lacking in its anti - submarine ( ASW ) capacity . Specifically , it needed new hulls designed to anti - submarine warfare , and it needed them fast . The decision was to use the " Ytattack - 81 " project and modify it for ASW operations , as designing a completely new ship is a time - consuming and costly task . It was given a towed array sonar , ASW torpedo es and the ELMA anti - submarine grenade launcher system . HMS " Stockholm " was launched 22 August 1984 closely followed by HMS " Malmö " 23 March 1985 , both ships entered service 1 May 1986 . In the middle of the 1990s the ships started to show their age , mainly because of their high mileage and the latest few years explosive development of electronics . The " Stockholm " class was a successful design and the ships ' basic status was good despite a hard life so the Swedish Defence Administration decided to give the ships a second life . HMS " Malmö " was the first to be modernised in 1999 with HMS " Stockholm " following suit 2000 . The modernisation included new engines , combat control systems , fire control systems , SIGINT and navigational systems . The ships both went through extensive modification of the mast , hull and superstructure to reduce their radar cross - section . Much of the modification was also made with low maintenance in mind to minimise the need for expensive repairs in the future . The guiding principle for the project was to update as much of the systems as possible to the same level as the Visby Corvettes . Both ships are back in operational condition now , attached to the 31 ' st Corvette Division of the 3rd Naval Warfare Flotilla . In early 2009 the Swedish government decided that the two ships in the class was to join the EU - lead taskforce outside Somalia , where its would fight piracy . In May 2009 the ships started their first patrol outside the Somalian coast . On May 26 HMS " Malmö " responded to a pirate attack on the Greek ship M / V Antonis . The Corvette fired warning shots with its 57mm canon and arrested seven pirates .