I've got a feeling that adding special slot type for PD was uncalled for, and they were better as S-slot things for three reasons:
- Being generally inferior to flaks, only corvettes could make decent use of those and yet they can't.
- You are forced to have those if you want implement carrier design on cruiser or battleship, yet flak does better.
- Even if you need PD, you are forced to go with quite specific hull design, which limits you again. Want PD on cruiser? - Go with hangar, despite the fact that you don't need hangar at all.
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