Can someone please explain what the heck you're talking about to the Marine in the room?
The basics...
Conditions of water tight doors/hatches inside a ship. In port they're pretty much all open to allow free passage up and down through decks as well as forward and aft. Their being open allows free passage by the crew to get in and out of spaces and up and down through decks.
In a general quarters/combat situation underway they all get closed to minimize spread of fire/flooding due to battle damage. Their being closed prevents the crew from moving around freely/quickly In the ship.
When a ship is away from the pier during peacetime the doors and hatches are set closed somewhat between the two. Usually above the waterline they're open but below the water line they're kept closed. This helps prevent fire/flooding in the events of shipboard accidents and collisions with ground and other vessels.
Obviously opening large heavy hatches going up and down decks places the members of a crew at risk of not being able to escape in the event of a fire/flooding so the vertical hatches have small, closeable cutouts in them that allow people to fit through.
They've got a letter code corresponding to the conditions of that hatches depending on what situation The ship is in... you may remember the big metal doors on the ship during your stays for CQ (on the O3 level moving forward to aft and going down the ladders to Big XO country and the wardroom downstairs).