The Sunken Submersible resembles a slightly larger version of the Submersible and even includes an open hatch. The Sunken Submersible can be found underwater via a Submersible. The interior of the structure can only be accessed via swimming, and is completely empty. While the structure resembles the drivable submarine, it does not feature a front porthole. The entire exterior of the vehicle is completely rusted and covered with barnacles and seaweed. The structure is located near an arrangement of pipes, but is distinct from all of the structures and undersea lofts around it. While the location of Frank Mathers' submarine is never seen in-game, there is a possibility that the structure could be part of it. There are also symbols on the sides of it. Unfortunately, the symbols are too dirty to decipher. It is never referenced or mentioned at any point in the game's storyline. It is possible that the sunken submersible is just an Easter egg from Rockstar to congratulate the players who spent their time searching for hidden things in the ocean.