The game only allows one player-controlled "Deck Gun", so if the AA guns are set to "Deck Gun", you might not be allowed to control them, since you already have control over the main gun. The "camera" might be the only reason you're allowed in the position. That would be a test to try, is a non-threatening enemy ship, such as an un-armed tug anchored nearby to the player sub, and then an airplane come by a minute later, and see what you can and cannot do. Of course, standing orders out of CenPac state that you should NOT be caught unawares by any airplane under any circumstances...
