What is the range for the intercept fighter mission?

I believe that all ground units that are air-intercept capable can protect in a radius 2 hexes around them. According to research done by Oak, air units can intercept anywhere in their attack range. A single ground or air anti-air unit can only intercept once per turn. Interception does not guarantee destruction, and it's possible that your unit will still be injured or destroyed even if the intercept is successful.

My strategy when assaulting a naval stronghold such as this is to bring overwhelming force, and plan to lose a few units. (This strategy would certainly be historically accurate...)

If air units are an issue, are you bringing in adequate ground-to-air (and/or sea-to-air) defenses? Carriers can store fighters that can intercept enemy fighters attacking your land and naval units.

I would suggest setting up some carriers and other ships to protect your embarked land units from enemy air and sea units while they get into position. It's not 100% clear from your question, but you are aware that you can attack the city while embarked, yes? Otherwise you've got another turn delay where your unit is vulnerable when you disembark.

As I suggested in the comments, I'd also consider choosing a different tactic or priority target if you can. Small 1 or 2 hex island cities aren't generally high value targets, and their production pales in comparison to a city near forests and hills. Plus, they're hard to assault (as you've noticed) and if the map isn't all islands, fighting the brunt of their forces in a sea/air engagement by building a bunch of ships you don't have a use for once you capture the islands might not be the best use of your military resources.

If you can bypass these islands, you might be better off capturing some of their higher value cities inland, thereby crippling their war machine. Who knows, they may even offer you the islands when they beg for peace... :)

Air interception is based on the range of the fighter. If you promote the unit with range (+2). You are increasing the range at which the fighter will intercept other fighters. Interception range is at the hex the enemy is attacking, not the flight path taken.

As Oak says in the comments below... "interception doesn't stop the plane from attacking, it only damages it while it attacks. So your embarked units could have still died even if their attackers were intercepted."

I wish to add to that.,I have observed less damage on the target when my fighter is intercepted by another fighter or by other defences that is not the target, e.g. Destroyer. Untested, you could assume from that statement that a pack of destroyers (DS) is better than one because any one DS would have reduced damage as it is being defended by other the DS.

Captured Scenario

I managed to capture with save and load two scenarios where the enemy fighter was attacking one of my destroyers. Scenario 1 shows the fighter in range to defend the destroyer. Scenario 2 shows the fighter is just our of range.

Scenario 1.A - Fighter on carrier is in range to defend the destroyer. Larger Img

Scenario 1.B - My fighter (yellow circle) is defending my destroyer from enemy fighter (red circle). Larger Img

Scenario 2.A - I loaded the game and moved my carrier so the fighter was now out of range to defend my destroyer. Larger Img

Scenario 2.B - The enemy fighter (red circle) attacks my destroyer. My defensive fighters remain on the carrier eating ice cream. Larger Img