It included terms which limited the size of naval vessels on Ladoga to 100 tons, and the calibre of their armament to a maximum of 47 mm.
When the Finns embarked on their naval rebuilding program in the early 1930s, some vessels were purposely designed to fit this 100 t limitation, including a small submarine.
The Winter War began on 30 November 1939 when the Soviet Union attacked Finland, nullifying the Treaty of Tartu.
The Finns hastily gathered a small flotilla, consisting of the icebreaker Aallokas, the improvised gunboats Aunus, Vulcan and Tarmo, as well as Hercules, Kiviniemi, Yrjö, Voima, S I, N K af Klecker and a number of transport vessels to protect its sea front and islands.
There were no major naval battles in the open waters of Lake Ladoga during 1939 - 1940, so the fleet units were tasked with fire support against the attacking Red Army, and spreading mines along the coastal areas.
These were used already on 16-17 August 1941 to mount a landing operation on Markatsiman (ru: Ostrov Markatsiman-Sari) island which was lightly defended and fell quickly.
After the Finns had captured maps of the Soviet naval minefields on the lake several boats were detailed for minesweeping duties which yielded no results nor losses.