system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why don't people run out of air in a submarine?

It makes perfect sense in an airplane or car, but how does it all work underwater? Do submarines have air conditioning? Is air recycled or does it have something to do with the water?
gpt
Modern subs have machines called Electrolysers.  Basically, these machines take seawater, and split up the hydrogen and oxygen molecules and the oxygen is then stored in tanks for use.  Subs also have scrubbers that remove CO2 and recirculate the oxygen from when we exhale.