Built as Russian Voin and taken over as M-1 by Finland when the country declared independency in 1918. 1936 renamed Louhi.

On 3 Jan, 1940, the S-2 hit a mine and sank off Märket lighthouse, Åland Islands. The minefield of 190 mines had been laid by Louhi in December 1939. 

At 11.50 hours on 12 Jan, 1945, an explosion occured under the Louhi that was returning with the Finnish minelayer Ruotsinsalmi from a minelaying operation south of Russarö (160 mines were laid) under escort of two Soviet MO-class submarine hunters. The ship sank within two minutes and the survivors were picked up by the escorts shortly thereafter. A long time it was believed that the vessel probably hit a mine from a deep laid Soviet barrage in the area because no German claim could be found. But years later the wreck was located in 40 metres depth and shows signs of a torpedo explosion. U-370 had reported an unsuccessful attack with two Gnats on a group of warships in the area on that day, so it is very likely that one of the Gnats had in fact hit the minelayer.

This was the last U-boat success in the Baltic Sea.