The rebreather is one of the few items required to finish the game.The patchnotes for v0.14 suggest that more spawn locations for the rebreather will be added later.The rebreather appears to be based off an Dräger FGT 5400 rebreather.It is attached to a skeleton, and it is surrounded by some air canisters. It is to the left as you approach the water hole. It is found right before a water hole inside the cave.
The rebreather currently can only be found in Cave 5 - Submerged Cave, near the southern entrance. Whilst having the rebreather equipped underwater, you do not gain athleticism. When the rebreather is equipped and the player is submerged in water, the mask will provide light much like the flashlight, further aiding underwater navigation. Note that the rebreather can only be equipped while on solid ground as the inventory cannot be opened otherwise. Once collected, the rebreather can be found in the upper left corner of the inventory, directly behind the backpack. There are also two canisters directly next to the rebreather when you first find it. The rebreather uses air canisters for refilling (by pressing Left Mouse Button on the canister), which can be collected near many dive spots, for instance in the cave system and on the yacht. When equipped, the player's HUD changes and the field of vision is slightly impaired. There is currently only one hidden on the peninsula. The rebreather allows the player to dive underwater for extended periods of time by providing the ability use air canisters for breathing.