[neilep (OP)]

Dearest Submersible Supervisors,

How does the crew of a submarine that remains beneath the ocean top (For months) breathe ?.....

....is it as simple as just carrying a whole load of oxygen tanks ?...or do they send an umbilical upwards ?...or do they make the oxygen from the sea ?...or is all recycled and processed ?..or do they take oxygen fairies and shake them like salt and pepper ? !!

I don't know and I'm feeling lightheaded just thinking about it?

Doe ewe know ?...cos I don't !!

[another_someone]

The only submarines that can remain submerged for months are nuclear subs (diesel powered subs cannot remain submerged more that, at most, 24 hours).  That having been said, even diesel subs can remain submerged for longer, but at shallow depths, by using a snorkel that is pushed above the surface of the water to suck in oxygen.

Nuclear subs used to obtain oxygen from the surrounding water by electrolysis, but I don't know if they may now use filters that perform a function similar to fish gills to extract dissolved oxygen from the water.

[Quantum_Vaccuum]

would they extract the exceses amounts of CO2?

[daveshorts]

Yes, a traditional way is to react it with calcium hydroxide to produce calcium carbonate.

I am not sure how nukes get rid of the hydrogen they produce, as I think you could track the subs with it otherwise.

[another_someone]

Yes, a traditional way is to react it with calcium hydroxide to produce calcium carbonate.

I am not sure how nukes get rid of the hydrogen they produce, as I think you could track the subs with it otherwise.

Looking up information about Apollo 13, it was evident that they used lithium hydroxide rather than calcium hydroxide, and it was a limited supply of this (or at least, they had to improvise using the canisters from one module in another module, in which it did not properly fit) that was one of their concerns after the explosion.  I assume that lithium hydroxide was used because it would be lighter than calcium hydroxide.

Nonetheless, there would still be the problem that this has a limited capacity to absorb CO₂, and once that capacity has run out, they either need a mechanism to recharge the system (heat the carbonate with water to revert to the hydroxide?), or they would no longer be able to run submerged.

More recently, from what I can see, NASA has been using silver oxide, and solid amines, which can both be regenerated in a vacuum (readily available in space), to clear CO₂ and atmospheric humidity.