The one-flue harpoon or one-flue iron (sometimes "single" instead of "one" is used) is a type of harpoon used in whaling after its introduction in the early 19th century when it replaced the two-flue harpoon. Due to the asymmetric design of the head for which it is named, the one-flue harpoon was less likely to cut its way out of the whale meat and blubber, and was therefore more successful in whaling.