Rebreather

The  is a diving tool that recycles the oxygen that the diver exhales enabling a much longer time spent under water. While it does lengthen submarine travel, be wary that it isn't infinite and won't prevent drowning in the event that its reserves are depleted.
 * The increases the time you may stay underwater by 3 times as much before needing fresh air.

In-Game Description
This small device can get a little oxygen from the water. Be careful, it doesn't last long.