Finnish submarine Vesihiisi

Vesihiisi was a Finnish 500-tonne Vetehinen class submarine that was constructed in the early 1930s. The vessel served in the Finnish Navy during the second World War.

German Design Iku-Turso, Vesihiisi, Vetehinen
While preparing the design of the Saukko, the Germans also prepared a design for a seagoing submarine for the Finnish Navy. Three submarines were built to this design, and like the Saukko, they were fitted for mine-laying, the mines being supplied by the Germans. Being designed for use against Russian bases (never very far from the Finnish bases), radius of action was not of prime importance to this design, and only 20 tons of fuel oil were carried (as opposed to the 67 tons carried by the German Type VIIa based on this design.

Winter War
Vesihiisi was alerted with Vesikko 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.

Vesihiisi run aground in early December 1941 and had to be docked for a few days for repairs. On December 27 Vesihiisi laid 16 mines off the Soviet naval station of Paldiski but soon after the ice forced the submarine to stay in port.

Continuation War
Vesihiisi started the Continuation War on June 22 by laying 20 mines in Estonian waters (controlled at the time by the Soviet Union). She laid 18 more mines on June 24 at Ruuskeri SSW from Gogland and further 18 mines on June 26 SE from Bolshoy Tyuters. After this the mining operation was postponed and Vesihiisi laid the 18 already loaded mines finally on August 2 east of Osmussaar.

On July 2, 1941 Vesihiisi while patrolling east of Gogland encountered an escorted freighter heading east. Torpedo attack failed and the submarine suffered light damage from the escort's depth charges.

On August 5, 1941 Vesihiisi attacked a convoy transporting supplies to besieged Soviet garrison at Hanko. Convoy consisted of a transport vessel of Molotov class (Iosif Stalin class passenger ship) escorted by pair of large minesweepers and group of patrol boats. Submarine penetrated the escort screen and launched two torpedoes at range of 700 m while being between the target and the escorts. Neither of the torpedoes exploded and the escorts forced Vesihiisi to dive to the depth of 75 m. Though submarine did not suffer severe damage from the depth charges the repairs on the dock lasted for a week.

In December 1941 after the Soviets had evacuated Hanko the Finnish submarines were docked for the winter. During the sailing season of 1941 the Italian torpedoes the Vesihiisi used (Finnish designation T/40) proved to be unreliable. During 1942 Vesihiisi was upgraded with new 12-hydrophone listening arrays and equipped with depth charge rack capable of carrying 4 depth charges. Submarine was further modified by streamlining the tower and moving the 20mm gun up to the tower.

On 9 August 1942, the Vesihiisi was deployed along with her two sister ships to Mariehamn. Their mission was to conduct anti-submarine and escort operations in the Sea of Åland. In the evening of 21 October 1942 she torpedoed and sank the Soviet S class submarine S-7, near Lågskär in the Sea of Åland. The captain (Sergei Lisin) and four of the crew of the S-7 were then captured.

On 4 July 1944 Vesihiisi laid 20 mines between Moshchny Island (Lavansaari) and Seskar (Seiskari). Boat was attacked with depth charges by two Soviet minesweepers but was able to escape without any damage. Submarine laid further 18 mines north of Moshchny Island on 6 July 1944.