Jiggle if the player has minimal defenses deployed yes it is possible. So against inactives, navy is a very versatile way to raid for quick cash. Against a heavily defended player, while it may be possible, it will be extremely expensive and I wouldn't recommend it.
Navies were extremely useless many months ago, but now that you can customize your fleet compositions, you can squeeze enough offensive firepower into a fleet (at the expense of its defense of course) to have some effective attacks. The default naval compositions are useless and you should stay very far away from them.
Navy fighter planes and cruise missile ships are your most effective naval weapons for conquering lightly defended countries.