Respirators and chlorine
 

Possibly one to add to the damage/repair/trouble to contend with wishlist is damage to the batteries from depth-charges, when coupled perhaps with water in the bilges might be a release of chlorine gas, and the necessity of crewman having to wear crude respirators as damage is repaired - and until the boat can be ventilated.. Damaged batteries would also result in a loss of "charge".

Loss of electrical services, lights, compressor, bilge-pumps, radios, hydrophones etc could also be modelled giving crews more problems of a sequential nature to deal with, fix this, so that it can be used to solve that problem, enabling something else to be fixed in turn...

Oh, and please do something else for the "death screen". It always seems like an anticlimax after being hunted and depth-charged.

Nice idea!
But why do you forget about moisture (fog) and smoke form fire?

Try to uboat operate...
:haha:

https://i.imgur.com/AQiYc9O.png

Nice mock-up! That's the sort of thing I had in mind, it just adds to the claustrophobia! I don't think it should be a frequent occurance by any means as it requires cracked batteries leaking into the bilges with sea-water also present therein (or vice versa).

Other interesting areas would be the effect of depth charges going off below the boat causing the U-boat to sink violently (gas infused air confers less buoyancy, so a trimmed boat will sink like a stone in this scenario.) Basically what I'm after is generating situations to cause the crew more non-lethal problems to contend with, be it loss of electrical power, internal fires, fumes, smoke, CO2 management, chlorine, more progressive damage to U-boat to near misses, breakage of instrumentation, injury of personel, leakage of periscope glands and so forth.

At the moment it's more a binary situation, either everything is working - or you're suddenly dead...

I'm a little surprised CO2 isn't an issue already. The way it works in SH3 is pretty good, but can be improved upon.

If your crew fires lots of torpedoes while submerged, or does a lot of depth-changing, then the CO2 level could rise quicker (presumably the crew are stressed and working hard to do tasks).

Simulate also the engines "breathing" air from inside the sub depending on how hard they're working when the hatch is closed.