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.
In the context of whaling during the early 19th century, the one-flue harpoon or single iron (sometimes "single" instead of "one") replaced the two-flue harpoon and was used for this purpose.