the crew you put in those "barracks" actually go into the ship's hull, as they dont
operate guns theres no point on having them on the deck just to take shots.

those side slots are for your support crew (repairers, restorers etc)

I know it looks as though they're on the docks and not the ship, but they are

although I think of those side slots as random XP gaining positions, they DO affect
your ship. that means that when you get to the higher ships like CVs, BBs, and the
rest, those spots can be crucial to victory. such as a medic to keep your sailors alive
or a restorer to keep your ship afloat.