Central Pacific / Naval Supply
In the historical World War II, both factions fought over Central Pacific islands, for two reasons:
It was much easier/cheaper to base fighters on islands than on carriers, because carriers are much more expensive than landing strips, and pilots need an extraordinary level of skill to take off and land on a carrier’s tiny runways. Even a tiny, rocky island served as a huge force multiplier for a nation’s air forces – you could store a couple hundred fighters on a small island, which is as many fighters as might fit on three or four carriers, i.e. nearly doubling the size of your available air force for the theater.
It was much easier/cheaper to stash (and use!) depots of spare parts, ammunition, food, and diesel on islands than on dedicated supply boats, because an island depot is much easier to build, maintain, and access than a floating supply boat. Very few ships were capable of cruising around the Pacific for more than a couple of months at a time without at least a minor resupply stop to take on more fuel and other consumables.
In the OOB versions of Axis & Allies games, very few players fight over the Pacific, because it’s full of a bunch of 0-IPC territories that aren’t connected to anything interesting or useful. Sea-based fighters function exactly the same as land-based fighters, and ships have unlimited range; you can sail a ship from San Francisco and Tokyo to back, fighting in five combats along the way, without ever bothering to stop near a friendly island chain.
The “national objectives” that give players extra IPCs for holding certain combinations of islands can help restore some interest to that region of the board, but it winds up feeling somewhat artificial and disconnected from the interesting historical aspects of carrier-based warfare. You’re not taking Wake Island because you need it as a base or even to deny your enemy the ability to use it as a base; you’re taking Wake Island because a little card says it’s worth extra cash.
So here are a couple of house rules that might get players thinking along more historical lines in the Pacific, without too much added complexity.
(*) Fighters are reset to C8 A2 D3 M4. A fighter that takes off from a land territory and fights in a sea territory (whether via a combat move, scramble, or otherwise) gets +1 to its combat rolls (so, the fighter returns to the familiar A3 / D4 level). This helps encourage players to store their fighters on islands, instead of just putting every available fighter on a carrier. Incidentally, this tweak also makes it slightly harder for players to advance a stack consisting of nothing but infantry and fighters – without some artillery, tanks, or tactical bombers, it will be harder to wage an offensive war.
(*) To remain in supply, a naval unit must be in or adjacent to a sea zone that touches a friendly land territory. A naval unit that is out of supply gets -1 to its combat rolls and convoy damage (to a minimum of 0). For example, a submarine that was out of supply would attack at 1 and defend at 0. A combat unit that is reduced to a roll of 0 still functions as a normal combat unit, i.e., it can still be taken as a casualty when appropriate. Supply is checked at the moment that combat occurs. Only ships are affected by supply rules; infantry, marines, and planes still have their full combat value. This should help encourage players to seize at least a few islands in any region where they plan to fight naval battles, instead of sending a fleet deep into enemy territory and leaving it there.
(*) Intact naval bases provide supply for two sea zones in every direction. If you are two moves away from a sea zone with an operational friendly naval base, you are in supply.
I agree this should be addressed. On the custom map we use all islands are worth at least 1 IPC, which helps somewhat, but like you said, it’s only financial.
I like the supply concept you have. Instead of tampering with all the unit stats, perhaps you could say that no surface attacks can be launched unless a friendly land zone is located in an adjacent sea zone. (double that distance with a naval base)