The official season pass for "Fallout 4" is currently available; however, Bethesda Softworks has not yet given any announcement regarding the game's upcoming DLC. However, according to a report from Crave Online, there are now indications that the first DLC may be primarily set underwater.

According to the report, game modder "xxxdeathknight72xxx" has discovered a secret weapon in the code of the PC version of the game. The weapon is a harpoon gun that isn't being used in the game. The curious thing about it is that it shoots out bubbles along with the main ammunition, hinting it was meant for underwater use.

Because the weapon is already in the game, all it takes to unlock is a simple console code. Ammunition is not found lying about and can only be acquired via cheat codes as well. However, because both already exist in the game's code, it is implied they were intended to be used in the released product or perhaps in future content such as DLC.

Several months ago, a Reddit post also pointed out a "Fallout 4" concept art that heavily hints at underwater sequences. Some of the images showcase a submarine, a person standing underwater, a first-person view through a diving helmet, and what appears to be a power suit underwater.

However, according to GamingBolt, there is also the possibility that these are merely segments of content that was intended for the original game's launch but were eventually cut from the finished product either due to design issues or time constraints. 

Many games have items and codes that were scrapped during the design process but somehow left in the game. The secret harpoon weapon might be a similar instance or, as the modder suggests, it could be an implication of future content.

At the moment no DLC pack has yet been announced but the season pass is available for now $30 on all three platforms: PC, Xbox One and PS4.