>aircraft carrier

Having served on both, this is actually a pretty interesting comparison (at least to me).

Carriers are simply larger, so they likely win by scale, but im not sure on a more per-(sub)system basis.

Carriers have a lot of aircraft handling systems that subs dont, elevators and hangers. Also the carrier has group c&c stuff.

Subs have a lot of stealth systems carriers don't, being that they're visible from space. Lots of dive related stuff, o2/co2 handlers.

They both have weapons systems, hvac, propulsion, distillation, steam generators, reactors, air compressor, many others.

Not obvious to me which one is more complex!