Vesikko is a submarine (the single ship of her class), 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 (a German front company) in 1930 as a commercial submarine prototype. Purchased by the Finnish before the war, she saw service in the Winter War and World War II, sinking the Soviet merchant ship Vyborg as her only victory. After the cease-fire with the Allies in 1944, Vesikko was retired. Finland was banned from operating submarines after the war and she was kept in storage until she was turned into a museum ship.
Vesikko was one of five submarines to serve in the Finnish Navy. The other four were the three larger Vetehinen-class boats Vetehinen, Vesihiisi, Iku-Turso and the small Saukko. The word "vesikko" is the Finnish name for the European mink.
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 terms of 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, the sale was cancelled and Vesikko was conveyed to the Military Museum.
The Military Museum moved Vesikko to Susisaari island in Suomenlinna, on the shores of Artillery Bay, and restored the submarine. The 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.