Realised that most modern submarines (and some aircraft carriers) use nuclear power, but destroyers and frigates don’t. I don’t imagine it’s a size thing, so I’m not sure what else it could be.
In: Engineering
The most simple answer is that a submarine survives by staying undetected.
Surfacing to refuel makes that difficult. So having a functionally limitless power source makes the need for surfacing (at least for fuel) unnecessary.
It also vastly extends their range as there is no need for refueling infrastructure/pre-positioning.
By comparison, surface ships are already on the surface, and are more plentiful in number than submarines. The cost to outfit that many would be significantly higher, while the advantage gained would be lower.
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