At 11.50 hours on 12 Jan 1945, an explosion occured under the Louhi that was returning with the Finnish minelayer Ruotsinsalmi from the minelaying operation Vantaa 3 south of Russarö under escort of two Soviet MO-class submarine hunters. The ship sank within two minutes and the survivors were picked up by the escorts shortly thereafter. A long time it was believed that the vessel probably hit a mine from a deep laid Soviet barrage in the area because no German claim could be found. But years later the wreck was located in a depth of 40 meters and shows signs of a torpedo explosion. U-370 had reported an unsuccessful attack with two Gnats on a group of warships in the area on that day, so it is very likely that one of the Gnats had in fact hit the minelayer.

This was the last U-boat success in the Baltic Sea. The mine barrage Vantaa 3 consisted of 160 mines in two lines and in the following weeks U-745 (von Trotha) and U-676 (Sass) were both lost with all hands after hitting mines south of Hanko.