Secret Fallout 4 Harpoon Gun Points to the Possibility of Underwater Combat

Modder xxdeathknight72xx found this weird and powerful harpoon gun in Fallout 4. When fired, the gun's animation includes a stream of bubbles, which implies the gun was designed for underwater combat. Also, it's a harpoon gun, so, you know, that would make sense. Could it be for some upcoming DLC? Or was it part of some scrapped underwater area? Only time will tell!