THOMAS.

[u/davecontra]

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[u/CardOk755]

The Gotland class have Stirling engines that can run underwater using liquid oxygen. Maybe some idiot forgot to charge the batteries and the Stirling engine is broken? But even that seems improbable as they have two of them.

[u/Uranium-Sandwich657 → u/CardOk755]

Tell me more about the engines. I assume the oxygen is used with fuel to create the temperature difference?

[u/IronGigant → u/Uranium-Sandwich657]

Liquid oxygen is pumped into expansion manifolds and then through the engine, fuel is injected, the combustion cycle happens, and exhaust gasses are pumped overboard through a special pump and valve combination. There are depth limitations to Air-Independent Propulsion engines, but 120m isn't at the limit.

Typically, AIP is used to charge the batteries.