On August 22, 1943 at 5.30 am, Riilahti set out from Loviisa on an anti-submarine mission west of Hogland. The patrol vessel VMV 1 followed her on the journey. 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. While the vessel tried to start her engines and reach steering power, the Soviet motor torpedo boat TK 94 fired a torpedo, which struck Riilahti amidships and broke her in two. Riilahti sunk in two minutes, taking with her 23 of her crew. VMV 1 saved eleven men from the water, one being the commander of the ship, and Mannerheim knight Osmo Kivilinna. He later died from his wounds on the operating table.
