Swimming: Underwater operations require their own unique set of skills that must be developed by an agent with extreme physical dedication.
Oxygen duration (s)
An agent can swim normally.
The swimming speed and lung capacity of an agent increases slightly.
The swimming speed and lung capacity of an agent increases moderately.
An agent moves like a dolphin underwater.
This skill determines how long JC Denton can stay underwater, as well as how fast he swims. While it's generally considered one of the game's less desirable skills, thanks to its situational nature, upgrading it atleast once can actually prove to be quite beneficial, since it's cheap and provides a dramatic boost to speed underwater. Later levels are a bit redundant, though the higher breath duration does let you evade enemies for longer in some situations.