Finnish submarine Vesikko " Vesikko " is a Vesikko - class submarine , which was launched on 10 May 1933 at the Crichton - Vulcan dock in Turku . Until 1936 it was named by its manufacturing codename CV 707 . " Vesikko " was ordered by a Dutch engineering company Ingenieurskantoor voor Scheepsbouw in 1930 as a commercial submarine prototype . " Vesikko " was one of the five submarines to serve in the Finnish Navy . The other four were the three larger Vetehinen - class boats " Vetehinen " , " Vesihiisi " , " Iku - Turso " ( named after Finnish mythology characters ) and the small " Saukko " ( Finnish for otter ) . The word " vesikko " is the Finnish name for the European mink , a small predator now near extinction ( already extinct within Finland ) . History of Vesikko . Part of the Development of German submarine fleet . Ingenieurskantoor voor Scheepsbouw or IvS , which was actually a German company in the Netherlands , was established for designing a new submarine fleet . According to the Versailles Peace Treaty , Germany could not have various weapons , including submarines , after World War I . This resulted in moving the armaments ' research to foreign countries . For example , German tanks and aircraft were tested and developed in the Soviet Union . In other words , unlike the other submarines in the Finnish Navy , " Vesikko " was not part of the Naval Act . Instead , it was part of the secret rebuilding of the German Navy . The objective of Germans was to design a modern submarine type to be used during general mobilization ; technology and standards were to be new and not based on World War I designs . For this purpose two prototypes were built , E1 in Spain and CV 707 in Finland . The latter was later chosen as a first submarine type for the new fleet . Construction of both of these experimental submarines was funded by Reichsmarine . Commander Karl Bartenbach , who had retired from active service in the Reichsmarine , worked as secret liaison officer in Finland . His official title was Naval Expert of the Finnish Defence Forces , and it was under his leadership that the 496 ton Vetehinen - class and the 100 ton Saukko - class were built in Finland . Both submarine types were designed by IvS . For German Navy , his mission was to oversee the developing and construction of a 200 – 250 ton submarine , which would still equal the combat effectiveness of the 496 ton Vetehinen - class . The whole task was named The Liliput Project . The official decision allowing " Vesikko " to be constructed in Finland was made in 1930 after several meetings with the Finnish Government . Because The Liliput Project broke agreements of the Versailles Peace Treaty , there was no mention of Germany in the document , and it was decided that the new submarine could only be sold to nations belonging to the League of Nations . The would - be buyers also had to have the rights to own such a weapon . The Finnish Government gained primary rights to purchase the submarine . The construction of CV 707 begun in 1931 at the Crichton - Vulcan dock in Turku . After its construction , CV 707 became one of the most advanced submarine designs of its time . For example , the maximum depth was over twofold when compared to earlier German submarines , and its hull could be built completely by electric welding , without rivets – this increased resistance of water pressure , decreased oil leakages , and made the construction process faster . Germans tested CV 707 in the Archipelago of Turku during the years 1933 – 34 . " Vesikko " is a prototype for the German Type II submarine s . Six Type IIA submarines ( U - 1 – U - 6 ) which were almost identical to " Vesikko " were built in the Deutsche Werke dock in Kiel , and after these , 44 Type IIB , IIC , and IID submarines were built before and during World War II . " Vesikko " is bought by the Finns . According to the agreement between the Finnish Ministry of Defence and the Crichton - Vulcan , Finland had the primary purchase option until 1937 , and the Finnish Government took over the submarine during August 1934 . After the Finnish Parliament had approved the acquisition in 1936 , the submarine joined the Finnish Navy under the name of " Vesikko " . Actions during wartime . Winter War . " Vesikko " was alerted with " Vesihiisi " to Hanko region on 30 November 1939 as several Soviet surface combatants were headed towards the area . Submarine however failed to arrive to the area in time to intercept the Soviet cruiser " Kirov " and its escorts . " Vesikko " was able to get close enough to see the cruiser but was unable to reach firing position as it had to evade the shell fire . When on 17 December and on two following days Soviets sent " Oktyabrskaya Revolyutsiya " to bombard Finnish positions at Koivisto Finnish Navy decided to send out " Vesikko " to hunt for the large prey . However by the time submarine reached the area a day later the Soviet battleship " Marat " which bombarded on that day had already departed and temperature had dropped to −15 degrees Celsius which prevented the submarine from diving . Continuation War . In the summer 1941 all Finnish submarines were once again readied for combat operations and they sailed to the staging area in the Gulf of Finland . " Vesikko " ' s base of operations was to be Vahterpää island near the town of Loviisa . When the Continuation War started on 25 June , all submarines were ordered to patrol the eastern part of the Gulf of Finland . On 3 July 1941 Vesikko sank a Soviet merchant ship named " Vyborg " east of Gogland island . The attack was made 700 meters from the target ; first one torpedo was launched at 13 : 25 which hit the stern of the target . Target stopped but did not appear to be sinking so " Vesikko " fired another torpedo which failed to explode . Very soon after the strike , three Soviet patrol boats started to chase " Vesikko " and tried to destroy it with depth charges and salvage the damage ship but failed to accomplish either task . " Vyborg " sank on 3 July at 14 : 15 . Soviet historiography later downplayed the sinking of " Vyborg " , insisting that several submarines and German naval bombers had assaulted the ship simultaneously , and that over twenty torpedoes had been launched against it . During the fall 1941 " Vesikko " operated from Helsinki and made three patrols to the coast of Estonia . In 1942 equipped with depth charge rack , she acted as an escort to convoys in the Sea of Åland , and hunted suspected hostile submarines near Helsinki . In the beginning of June 1944 , " Vesikko " escorted the convoys which were evacuating people from the Karelian Isthmus . Due to the armistice between Finland and the Soviet Union , " Vesikko " was ordered to return to the port in 19 September 1944 . Vesikko sailed the last time as a combat vessel of the Finnish Navy in December 1944 . During wartime , several officers worked as the commanders of the submarine : Ltn . Kauko Pekkanen ( 1939 ) , Capt . Ltn . Olavi Aittola ( 1940 and 1941 ) , Capt . Ltn . Antti Leino ( 1942 ) , Capt . Ltn . Pentti Airaksinen ( 1942 ) , Capt . Ltn . Eero Pakkala ( 1943 ) , Capt . Ltn . Olavi Syrjänen ( 1943 ) , and Capt . Ltn . Lauri Parma ( 1944 ) . From Combat Vessel to Museum . In January 1945 , the Allies ' Commission responsible for monitoring the observance of the Peace treaty ordered the Finnish submarines to be disarmed , and in 1947 according to the Paris Peace Treaty , the Finnish Defence Forces were forbidden to have any submarines . The Finnish submarines " Vetehinen " , " Vesihiisi " , " Iku - Turso " , and " Saukko " were sold to Belgium to be scrapped in 1953 . " Vesikko " was spared because the Finnish Defence Forces hoped that Finland could in future gain permission to use submarines again , and " Vesikko " was then meant to be used for training purposes . " Vesikko " was stored at the Valmet Oy dock in Katajanokka district in Helsinki . In 1959 , the Finnish Navy decided to sell " Vesikko " because Finland had not managed to obtain the right to use submarines again , and because Valmet Oy complained that the old submarine hampered the work in the dock . Thanks to the Institute of Military History and the former submarine officers , sale was cancelled and " Vesikko " was conveyed to the Military Museum . The Military Museum moved " Vesikko " to the Susisaari island in Suomenlinna , on the shores of the Artillery Bay , and restored the submarine . Restoration process lasted over a decade and was very difficult ; most of the equipment had been removed after the war and put to other use . In addition , " Vesikko " had been subject to vandalism in the dock . However , with donations and voluntary work , the restoration was completed , and " Vesikko " opened as a museum on the anniversary of the Finnish Navy 9 July 1973 .