A Fallout modder has discovered Secret Harpoon Gun weapon in Fallout 4. It was discovered when modder “xxdeathknight72xx” was going through the files of Fallout 4 (developer might have included it during closed beta of some sort), and this means that Bethesda have some plan to release it as DLC or seems to have completely scrapped it.
This Harpoon gun override the “Railway Rifle” and it, and it works as a Harpoon should, reload animations works properly and there is a trail of bubbles coming off the harpoon, a major hint that Bethesda might have some bigger plan for a submarine-type combat in Fallout 4. You can check out the footage from YouTube user Tyrannicon showcasing the working of this mod.
To add this weapon in your arsenal, you need to download this mod. This modder has created his own Normal map and Spec map for the weapon. The only bugs in it is “Ammo is not able to be picked up so you will need to add ammo by opening the command (press ~) and enter player.add item 000fe269 50”
Please Note: This is not a fully developed weapon and was obviously not put into the game by Bethesda for unknown reasons. So install at your own RISK.