I was expecting to see one. You could have a lot of fun (visually) with the transferring room between underwater and inside the vault.
Hopefully once the GECK drops, modders will do a few and they'll be approved for us console people.
Well, they have or had something planned for underwater. A modder found in the files, a harpoon gun.
http://www.gamespot.com/articles/secret-fallout-4-harpoon-gun-discovered-by-modder/1100-6432498/
Dang. Wrong coast. But finding a piece of an oil rig would be a nice nod to F2. as would finding the wreck of Frank's Power Armor.
IIRC there was an underwater city in Morrowind or was it Oblivion......hmmm?
It wouldn't surprise me if there is an under vault some where, but all the water bodies I have come across are kind of shallow to hold a sunken vault.
I saw that too! except i tried to talk to her and, i guess due to her grief, she lashed out and tried to shoot me. so now she gets to share that grave.
One of Bethesda's DLCs for Fallout 4 better be water-themed. That's all I'm saying.