4. HOW DO SUBMARINES / SUBMARINERS BREATHE UNDER WATER?
Submarines are either diesel/electric (Conventional) or driven by a nuclear reactor (Nuclear).
Diesel-Electric Submarines
When a diesel-electric submarine shuts its hatches and submerges it captures sufficient air inside for its crew on a patrol and, when operating near the surface, draws in extra air by raising its snort mast head (like a schnorkel) above the water. It takes a lot of air to run the diesels when operating on or near the surface. The diesels also drive generators creating electricity to charge the submarine batteries that are used to power the submarine when submerged below snorting depth.
When a diesel submarine is under water, air conditioning and dehumidifying systems take in air from each room (compartment), cool it, dry it, and recirculate it. Carbon dioxide produced when the crew breathe out is dangerous if allowed to build up and is removed by passing the air through charcoal filters and special crystals to remove and neutralise any foulness.
Limited amounts of oxygen could be added to the air from storage bottles if required but reserves of compressed air are carried mainly to perform essential operations like surfacing, torpedo/missile firing and blowing out waste from tanks.
