I read a post somewhere concerning the uselessness of fighters. True. I've never seen one of my fighters shoot down an enemy bomber. Irritating. Except for recon misions. If you know enemy naval units are just outside your territory but cannot readily see them, you cannot bomb them with bombers unless you move a naval unit of your own within two tiles of the target. But suppose you have no naval units in the area. You do a recon mission to expose the target. But then you only get to do one bombing mission then the target disappears again.
OK now let's see the other side of the coin. Knowing you can't bomb them if you can't see them, You feel your destroyers are safe from air bombardment as long as they are two tiles away from the enemy's border. Ahaa! Not so! If you have a spy in the enemy's capital and know that there is only one fighter and no submarines in the AI's arsenal, it leaves you wondering why four of their bombers were just able to pound two of your destroyers in a location you believe to be unseen to them. No enemy naval units were within sight of my destroyers, and my spy informed me that they have no subs. Worse case scenario they do a recon mission then send one bomber. If the situation were reversed, that's your best case scenario. These rules somehow don't apply to the AI, though. In conclusion, AI bombers can see you no matter what.