|The following is based on Fallout: Brotherhood of Steel 2 and has not been confirmed by canon sources.|
The underwater suit is a piece of clothing in Fallout: Brotherhood of Steel 2.
For those days when you really need to walk on the ocean floor. This handy-dandy scuba kit lets you enter the underwater level, where you'll have to fight mutant piranhas. It resembles the old metal 50s diving suits.
The underwater suit would have allowed the player character to traverse the five medium to large underwater maps at the ruins of Corpus Christi, which has been partially flooded by the rising of the Gulf of Mexico after the Great War.