The submarine Vesikko (named as CV-707) was a submarine of the Finnish Navy in World War II, served as a direct prototype for German Type II U-boats. Vesikko was one of five submarines to serve the Finnish Navy.

It was built in Turku and launched in May 1933. It was designed by Dutch Ingenieurskantoor voor Scheepsbouw den Haag (I.v.S) and built in 1933 by the Crichton-Vulcan shipyard in Turku, Finland. It was part of the secret rebuilding of the German Navy. After its construction, CV 707 became one of the most advanced submarine designs of its time. 

Between the years 1933 and 1934 the German Navy carried out trials with the submarine in the Turku Archipelago. In 1936, the Finnish Navy bought it and named it as Vesikko.

Vesikko belonged to the Finnish Navy as one of five submarines in the 1930s and 1940s and undertook patrols in the Gulf of Finland during the Winter and Continuation Wars (1939–40 and 1941–44). The base for Finnish submarines was in the dock area of Suomenlinna.

Like other submarines of the Finnish Navy, she operated and patrolled the Gulf of Finland in convoy, safety and patrol duties during the Winter War against the Soviet Baltic Fleet. On December 1 and 19 December 1939, Vesikko made attempts to attack the Soviet heavy cruiser Kirov and battleship Marat, both of which had been damaged by Finnish coastal batteriers.

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. During Continuation War until her end, Vesikko operated making patrols, escorting to convoys and evacuating people from at the end of war.

As the Paris Peace Treaty of 1947 forbade Finland from having submarines, the Finnish submarines were scrapped, with the exception of Vesikko. She was lying as a wreck for years. It was eventually put up for sale for anyone willing to buy it. Fortunately former crew members of the submarine managed to rescue and restore it. Vesikko was restored as a museum, showcasing the cramped working and living conditions of its wartime crew and opened to the public in 1973.

The submarine currently lies on the island of Suomenlinna. It has served as a museum during the summers since 1973 as a part of the Military Museum of Finland. Vesikko is the last surviving Type II submarine in the world.