The stock game (and most of the mods for it) have the visual "fog" settings set too close in distance for an average "clear day" day.
A good test is to simply start a new Campaign from Pearl Harbor.....starting at the "at sea" position. Compare your view looking back at Oahu Island over your right shoulder. It's only about 5nm from shore:
Yet, you won't see the island. The game has the terrain fogged in too much. There's no reason why on a clear day, a 5nm object (like an island) should not be capable of being seen.
I've got comparison images, found
HERE, from my [WIP] Day of Infamy mod thread regarding this very issue. It's my intention to fix this issue with the new mod.