Finnish submarine Iku - Turso Iku - Turso was a 500 - tonne submarine that served in the Finnish Navy during the Second World War . It was launched in May 1931 and was named after a Finnish sea monster , Iku - Turso . It was built by the Crichton - Vulcan shipyard in Turku according to a project developed by NV Ingenieurskantoor voor Scheepsbouw , " IvS " , and was scrapped in 1953 . Combat history . Winter War . On 7 December " Iku - Turso " was sortied to intercept the Soviet freighter " Ivan Papanin " sailing from Stockholm . The submarine was informed of the departure time of the target and the likely route and so " Iku - Turso " patrolled in the international waters off Sandhamn and Svenska Högarne during the night . Unidentified patrol boats harassed the submarine and forced it to dive and by the time " Iku - Turso " was able to reach periscope depth there were no freighters in sight . The " Ivan Papanin " had passed the area few hours earlier and likely having been warned of the presence of the Finnish submarine , it had altered its course to evade " Iku - Turso " . In late December 1941 " Iku - Turso " patrolled for a couple of days off Liepāja but did not encounter any targets the rules of engagements would have allowed the submarine to attack . In January 1941 " Iku - Turso " patrolled four days off Saaremaa and Hiiumaa but without any luck . Continuation War . On 22 June 1941 the " Iku - Turso " laid 20 mines north of the island of Mohni / Ekholm . A further 20 mines were laid at Ruuskeri SE from Gogland on the 24th and 18 mines to south of Vaindloo on 26 June after which further minelaying operations were postponed . " Iku - Turso " laid 18 already loaded mines on 11 July of the coast of Estonia east of Mohni . On 30 July " Iku - Turso " along with " Vetehinen " were sortied to intercept a Soviet convoy moving to and from the besieged base of Hanko . The submarines saw the convoy but were unable to maneuver to attack position . In December 1941 , after the Soviets had evacuated Hanko , the " Iku - Turso " was docked for the winter . Though " Iku - Turso " had not had much chance of using its torpedoes , the experiences from other Finnish subs were that the Italian torpedoes used ( Finnish designation T / 40 ) were unreliable . During 1942 , " Iku - Turso " was upgraded with new 12 - hydrophone listening arrays and equipped with a depth charge rack capable of carrying 4 depth charges . The submarine was further modified by streamlining the tower and moving the 20mm gun up to the tower . On 27 October 1942 , after unsuccessfully attacking a Soviet Shchuka class submarine with the 20 mm Madsen cannon in poor visibility , the " Iku - Turso " later came across and torpedoed another Soviet Shchuka class submarine . After the torpedo impacted , the target disappeared . On the impact site , the Finnish submarine located a large oil spill with even more oil still rising to the surface . The sunken submarine ' s identity has later been contested as several Soviet submarines of Shchuka class were lost at that time in the area but the most likely candidates are either " Shch - 320 " or perhaps even more likely " Shch - 308 " as some Russian sources claim that the " Shch - 320 " had been sunk by a mine earlier that month and that the initial unsuccessful attack by " Iku Turso " had been against " Shch - 307 " . On 30 July 1944 " Iku - Turso " attempted to attack a convoy targeting a tug but failed to reach firing position . On 24 August 1944 " Iku - Turso " ran into an obstacle — apparently an anti - submarine net - but was able to get loose . A mine which had been attached to the obstacle exploded but caused only light damage to the submarine .