Fallout 4 code contains a secret harpoon gun
If you're a modder rooting around in the assets behind the scenes of Fallout 4 you might be surprised to find that there's another such weapon lying just under the surface waiting for someone to notice. As has been reported by Kotaku and others, that's exactly what happened when modder xxdeathknight72xx went on a leisurely swim looking for inspiration in an already packed modding space and found the resources for a harpoon gun sitting unused in the Fallout 4 game code.
The harpoon gun can be added into the game with a mod to replace the in-game assets for the Railway Rifle and functions in much the same way, firing long harpoon shafts at almost ludicrous speeds, pinning enemy heads and limbs to whatever surface is handy even if it's a good 40 meters away on Mama Murphy's mailbox. Even more interesting is the bubble animation that pops out of the end of the barrel when you pull the trigger, indicating that this is the kind of weapon that was intended for underwater use.
Here's YouTuber Tyrannicon trying it out:
It's unclear whether this weapon is part of some scrapped mission or quest that never made it to the final cut of the game but the number of perks giving bonuses to players in water, as well as the huge number of rivers and lakes in-game, seem to indicate that Bethesda had something in the works as far as underwater gameplay goes.
The other option of course is that Bethesda still has plans in place to give players the underwater wonderland they've been hoping for, and that the harpoon gun is part of some future DLC just waiting to be unlocked. The concept of a Bioshock-esque jaunt through some underwater Vault experiment is at once a terrifying and exciting possibility.