Riilahti and Ruotsinsalmi began mining the Gulf of Finland on June 26, 1941, immediately after the outbreak of the Continuation War.

In 1941, Riilahti managed to seize control of a Soviet barge and participated in minesweeping operations south of the Hanko Peninsula.

She was involved in artillery duels with ships from the Soviet Navy, gave fire support to the Finnish defenders on the island and fended off several air attacks.

At 2 pm on August 23 an outlook spotted two Soviet motor torpedo boats and sounded the alarm.

The officer on duty had previously ordered the engines to be stopped so that the sonar operators easier could listen for submarine sounds.

VMV 1 saved eleven men from the water, one being the commander of the ship, and Mannerheim knight Osmo Kivilinna.

This was one of the most significant single losses during the war years; Kivinlinna was a very well-liked officer, and it was widely believed that he could become the first full Admiral of the Finnish Navy.