Apart from a work-up patrol in the Norwegian Sea, she spent the bulk of the war in the Mediterranean. While working up, "Unrivalled" fired a torpedo at what was thought to be a submerged enemy submarine. Only the periscope was sighted, and the torpedo was fired in the direction detected by the hydrophones, but no German submarine was in the area. Whilst in service in the Mediterranean, she sank a number of small merchantmen and small naval auxiliary vessels with both torpedoes and gunfire. These included the Italian auxiliary submarine chaser O 97 / "Margherita", the Italian merchants "Maddalena", "Mostaganem" and "Pasubio", the Italian tugs "Genova" and "Iseo", the Italian sailing vessels "Triglav", "Albina", "Margherita", "Sparviero" and "Ardito", the German auxiliary submarine chasers "UJ 2201/Bois Rose" and "UJ 2204/Boréal", the Italian tanker "Bivona", the small Italian merchant "Santa Mariana Salina", the Italian auxiliary minesweeper "R 172 / Impero" and the small Italian vessel "San Francisco di Paola A".