According to the 1920 Tartu Peace Treaty between Finland and Soviet Russia the displacement of any military vessel on the Ladoga Lake could not be more than 100 metric tons. Finnish lake submarine Saukko (Otter) was specially created for the operations on the Ladoga Lake having in mind this restriction.
Saukko was laid in April 1928 on the Helsinki "Hietalahden Sulkutelakka ja Konepaja" shipyard by the German project Pu110 (experimental prototype of the quick-assembly mini submarine) under the shipyard number SA 241. She was launched in July 2nd 1930 and finished in December 16th 1930.
Saukko crew consisted of 13 men. The outer hull had enforced ice shield. The submarine could be pulled down into two sections (stern with the engine and prow with accumulators). This allowed to transport her by railway (in this case the deckhouse was also taken away). The engine used was the experimental Krupp-Germaniawerft Diesel, found to be not quite fitting in exploitation. The submarine itself was also found too small and was left the only one built by the project Pu 110.
Initially there were plans to convey Saukko to Lahdenpohja by railway ant to include her into the Ladoga flotilla, but it never happened. During the wartime in 1939-40 and 1941-1944 the submarine acted in the Baltic Sea. Yet the Soviet intelligence new about the possibility of transferring her on the Ladoga lake and one of the tasks of the Soviet Ladoga flotilla before the Winter War was the organisation of the counter-submarine defence. (the order of the Baltic fleet Commander-in-Chief N 7/operational issued November 23rd 1939).
After the wars Saukko was put to conservation and in 1953 was destroyed.