I've suggested a new interception feature for the next game, and some people (including Vic) agreed that it would be a good thing to have. Now I'm wondering how it could actually work.
Naval interception means that a fleet or bomber force could be set to automatically intercept and attack enemy fleets within a certain range during the enemy's turn. The way AT works now, an enemy transport fleet could pass by my battleships and land troops on the coast without any danger of being attacked. Germany could capture London with three unescorted transports, although the entire Royal Navy waits in the channel. There isn't much point in occupying islands in the Pacific, because an enemy fleet can just sail straight from San Francisco to Tokyo, right past any number of airbases and fleets.
For starters, there already is the air interception function, where your fighters attack incoming planes. But there is a problem with that: If I have five fighters set to intercept but the enemy attacks with 15, it will result in my five being shot down, most likely without causing any losses. I can set the Loss percentage (retreat when this number of losses is reached during combat) to any value I like, with a 3:1 ratio against me, most of my planes will probably die without having a chance to retreat.
If that happens with naval interception, the feature breaks more than it mends. My destroyers should attack a sub, or my two cruisers should attack one enemy cruiser, but not a fleet of battleships. No suicide attacks. We'd need a setting which governs the strength ratio at which they will attack. Of course, if they miss a battleship or two during recon, that's tough luck but that's OK.
* At what range should interception be possible, i.e. where do the AP come from, your last turn or your next turn? Do you have to reserve AP for interception at the end of your move, or are they subtracted from your next turn's AP? Or does interception cost no AP (like air interception), but is limited in range (e.g. half your fleet's normal range)?
* When is it triggered? Only if the fleet itself spots an enemy fleet nearby? That would limit the usefulness of interception. Or is it triggered by any fleet being spotted by your side, as long as your fleet can reach the hex? The problem is, if your intercepting fleet is south of that hex where the enemy is spotted and the enemy is moving north, you probably won't catch them. But how would the game know that? It's difficult to design a rule and program it. There are lots of board games with naval interception rules, but AFAIK they all use a few large sea areas instead of hexes. It's more abstract but interception (and other things) are much easier to handle that way.
* Will your fleet always *find* the enemy, or is there a chance that their fleet slips through? I think there should be, but how good is it?
* About the strength ratio: fleets have Power Points, but the scenario designer should make sure that transports don't have PP. And because of AT's combat system, an intercept setting of "Attack only if 1:1 or better" could still result in three destroyers not attacking three subs because the subs have a slightly higher total power point rating.
* And I haven't even touched air-to-sea interception yet... sigh.