After the four submarines from the Naval Law of 1927, the fift Finnish submarine, Vesikko started life as private venture by Crichton-Vulcan shipyard in Turku, as an I.v.S:s covert operation to create prototype for the future German coastal submarines. Compared to the Vetehinen class, she was of new generation of construction with single hull, made mostly by welding, allowing theorethically deeper diving depth than the older boats. After completing as Cv-707 to the Crichton-vulcans private ownership, she was used clandestinely by Germans for sea-trials
in Finnish archipelago, before purchased by Finnish goverment and she joined the Finnish Navy under name Vesikko. During the wartime, it was generally regarded as best and most suitable of our submarines for the operations that were conducted, but despite this, its only victories came in summer of 41, when she sank a Russian merchantman. Postwar, as the peace treaty forbid submarines, Vesikko was the only one who was spared from scrapping, intially with hopes of early lifting of the treaty restrictions, so she could be recomissioned as training boat for new generation, but after this prostpect became unrealistic and the technology leaped foward, she was eventually refurbished as museum boat and is currently on display at Suomenlinna Garrison island in Helsinki.