In a recent game, I was trying to do amphibious invasions against a couple tiny-island cities the AI controlled. These two cities were spaced nicely between me and the long, skinny continent that the AI's main cities were located upon, although I could have bypassed them by going a long way around. The fact that they were located in such a defensive position made me attempt to take them rather than trying to form a beachhead and invade at a different location. In retrospect I should have attempted to buy out a nearby CS, land there, and then launch a navy-supported invasion across the land instead. That way I could have had multiple AA guns to defend the rest of the army. I should also note that I was using Thal's Vanilla Enhanced mod which makes the small islands more useful than automatic razes, but it also doesn't affect air missions as far as I know.
I did also forget that carriers could have escorted my fighters much closer to the invading infantry units.
I had one of the cities bombed down to 1 HP with battleships and destroyers, but I could never get an appropriate land unit close enough to capture it. Even when I had my fighters on the intercept mission and a few squares away from the embarked land unit, every turn that I had an embarked unit a turn from capturing, I'd get a message saying I was bombarded and destroyed by an enemy fighter. What radius does the intercept mission protect? Just the city itself?
Is there any other way to protect embarked land units for an invasion other than send like 6 units all at once and hoping a couple survive to take the city?
Best Answer
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... :)