Unique left Holy Loch after a refit, for a patrol in the Bay of Biscay on 7 October 1942. She left her escort off the Scillies on 9 October. No more was seen or heard from her after that date. was in the area on 10 October and reported hearing underwater explosions that led her to believe Unique was under attack, although the Germans made no claims of her sinking. She was reported overdue on 24 October 1942 when she failed to arrive at Gibraltar.