Vesihiisi was alerted with Vesikko to the Hanko region on 30 November 1939 as several Soviet surface combatants were headed towards the area.

On 27 December Vesihiisi laid 16 mines off the Soviet naval station of Paldiski but soon after the ice forced the submarine to stay in port.

[2] Vesihiisi commenced operations during the Continuation War on 22 June by laying 20 mines in Estonian waters (controlled at the time by the Soviet Union).

According to Finnish sources, the convoy consisted of a transport vessel of the Molotov class (Iosif Stalin-class passenger ship) escorted by pair of large minesweepers and a group of patrol boats.

[4] According to Soviet sources, there were only four minor ships: the 489-ton freighter Hilde, built in 1894,[5] one T58-class minesweeper, and two MO-class patrol boats.

[7][8] The captain (Sergei Lisin) and three of the crew of S-7; all of whom had been in the submarine's tower, were then captured (a fourth crewman drowned before he could be rescued).