On her twelfth and final war patrol, from 10 October-29 November, "Seal" again hunted in the Kurils. Her 30 days in the area yielded only two contacts worthy of torpedo fire. On 25 October, she caught and sank (5,742 GRT) killing 1,415 as it ran down the convoy lanes away from Paramushiro. Three weeks later, she attacked and damaged another maru off Etorofu (now Iturup). During the last days of the patrol, she ranged off the coast of Sakhalin, scoreless. On 17 October, she cleared the area.