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).

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 submarines. 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.

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.