The submarine was formally taken over by the Soviet Navy on 18 September 1940, by which time only five men of the submarine crew remained in place to instruct the new Soviet crews. After the outbreak of the German-Russian war in June 1941, "Kalev" was re-complemented, having a totally Russian-speaking crew, although the original name "Kalev" was retained. During the Second World War "Kalev" participated in military operations as part of the Soviet Baltic Fleet. "Kalev" did not return from her second patrol and was reported as missing since 29 October 1941.