Finnish minelayer Ruotsinsalmi Ruotsinsalmi was a minelayer of the Finnish Navy and the namesake of her class . " Ruotsinsalmi " was commissioned in 1940 and remained in service until 1975 . The vessel was named after the battle of Ruotsinsalmi , which was fought between Sweden and Russia in 1790 . New minelayers for the navy . Funding for two new minelayers had been secured as early as in 1937 , but instead the money was used to refurbish the garrison at Mäkiluoto . " Ruotsinsalmi " and her sister vessel , " Riilahti " , were intended as escort minesweepers for the Finnish navy ' s coastal defence ships " Ilmarinen " and " Väinämöinen " , and they were therefore designed with a draft of only 1 . 5 m . " Ruotsinsalmi " was armed with one 75 mm gun , one Bofors 40 mm gun s and two Madsen 20 mm anti - aircraft cannon s . The vessel had three mine dropping rails , and could carry about 100 mines . The ship could also hunt submarines , and was equipped with sonar , depth charge throwers and rails . The vessel was also strong enough to be able to tow mine sweeping equipment . It was equipped with smoke generator s so it could protect itself and other near - by vessels from the enemy . During the Continuation War . " Ruotsinsalmi " and " Riilahti " began mining the Gulf of Finland on June 26 , 1941 , immediately after the outbreak of the Continuation War . The first minefield , " Kipinola " , " Ruotsinsalmi " laid together with " Riilahti " south - east of Hanko which was intended to block Soviet seaways to Hanko . Same group laid already on June 27 the next minefield , " Kuolemajärvi " , north - west of Paldiski again to block route to Hanko . Another one , " Valkjärvi " , was laid on 29 – 30 June . " Ruotsinsalmi " together with " Riilahti " participated in ferrying the Finnish gunboats past Hanko in August 1941 . After two failed attempts by gunboats to rendezvous with minelayers on the nights of 25 - 26 and 27 – 28 August the minelayers penetrated the Soviet minefield and met with the gunboats west of Hanko and then escorted them through to Helsinki on 29 August 1941 . " Ruotsinsalmi " again with " Riilahti " were sent on 21 November to as minesweeping escorts for convoy of German ships consisting of two tugs and a depot ship headed to west through the Soviet minebarrier south of Hanko . However in the dark the convoy deviated from the swept route and as the sweeping gear became entangled with mines it had stop . Before the convoy managed to resume its journey , tug " Föhn " slipped outside of swept area and sank after hitting a mine but the rest of the convoy reached its destination . Voyage back through the minebarrier with a convoy of freighters started at midnight of 3 December after the escort group had been strengthened with German minesweepers " M 4 " and " M 7 " and it took place without any incidents . " Ruotsinsalmi " was Finland ' s most active minelayer during the Second World War , laying a total of 3 , 967 sea mine s and 541 sweeping obstacles . She was forced to lay mines against the Germans after the end of the hostilities with the Soviet Union in an attempt to hinder German submarine activity . She participated in the sinking of two Soviet submarines , ShCh 317 on 15 July 1942 ( along with VMV 16 ) and ShCh 408 on 25 May 1943 ( along with VMV 6 ) . After the war . " Ruotsinsalmi " had proven to be a sound design and well suited for its task . However , it continued to serve a number of different missions after the war . It ended its career as a diving support vessel ( 1973 – 1975 ) . She was mothballed in Upinniemi , and there were plans to make her into a museum , but she was scrapped at the beginning of the 1990s , after the owners had failed to gather enough funds .