I posted this on another thread that I started but I think it could be added to CIV IV or possibly the upcoming "Beyond the Sword" expansion. They are some suggestions on WWII air units game mechanics.
WW II Era Air Units
I’ve decided to try and create some guidelines and rule suggestions for WW II era air craft in CIV IV. Note, they are just that, guidelines and suggestions. Feel free to add other suggestions or critique. Thanks.
Air Units
Fighters: These units may be launched from land (within a city), a Military Air Base (Tile Improvement *) or from a carrier. Fighters can attack the following: Tile improvements, cities, ships and all ground based units. Fighters may be intercepted by AA batteries **, Fighters, Fighter Bombers, Destroyers, Cruisers and Battleships.
Fighters receive the following bonuses: +100% against all aircraft, -5% to city defence per hit/attack and an additional +10% collateral damage. Fighter bombers can also perform recon missions.
Statistics: Strength 12, Range 6, Cost 80 Hammers, Movement 2
Fighter Bombers: These units may be launched from land (within a city), a Military Air Base (Tile Improvement *) or from a carrier. Fighter bombers can attack the following: Tile improvements, cities, ships and all ground based units. Fighter bombers may be intercepted by AA batteries **, Fighters, Fighter Bombers, Destroyers, Cruisers and Battleships.
Fighter bombers receive the following bonuses: +50% against all bombers type aircraft (dive, torpedo, light and heavy bombers), -5% to city defence per hit/attack and an additional +10% collateral damage. Fighter bombers can also attack any aircraft and perform recon missions.
Statistics: Strength 16, Range 6, Cost 100 Hammers, Movement 2
Dive Bombers: These units may be launched from land (within a city), a Military Air Base (Tile Improvement *) or from a carrier. Dive bombers can attack the following: Tile improvements, cities, ships and all ground based units. Dive bombers may be intercepted by AA batteries **, Fighters, Fighter Bombers, Destroyers, Cruisers and Battleships.
Dive bombers receive the following bonuses: +50% against ground units, +50% against ships, -10% to city defence per hit/attack and an additional +20% collateral damage. Note: Certain dive bombers (such as the Junkers 87 aka: “Stuka”

may receive a +100 bonus against armour units (tanks, APC’s and other armour type units) specifically. Dive bombers cannot attack fighters or fighter bombers and may only defend against them.
Statistics: Strength 14, Range 7, Cost 100 Hammers, Movement 1
Torpedo Bombers: Like dive bombers, torpedo bombers may be launched from cities, a Military Air Base or from a carrier. Unlike dive bombers however, torpedo bombers can only attack ships as they were specifically designed to do so. Like dive bombers, torpedo bombers may be intercepted by AA Batteries **, Fighters, Fighter Bombers, Destroyers, Cruisers and Battleships.
Torpedo bombers receive the following bonuses: +100% against all ships except perhaps submarines. Torpedo bombers cannot attack fighters or fighter bombers and may only defend against them.
Statistics: Strength 15, Range 9, Cost 100 Hammers, Movement 1
Bombers: These units may only attack ground based targets as well as ships. However, they are not as effective at attacking the latter as dive bombers or torpedo bombers since the latter two types are more precise. Bombers come in two types; light and heavy. The light bombers may be launched from carriers or from a city or military air base. Heavy bombers can only be launched from a city or a military air base. Light bombers are also cheaper in cost and hammer production. However, heavy bombers possess a better range and attack strength and cause more collateral damage to ground based unit stacks and are better at lowering city defences.
Heavy Bombers receive the following bonuses: +100% against ground units, -20% to city defence per hit/attack and an additional +30% collateral damage. Both light and heavy bombers my attack the following: Tile improvements, cities, ships and all ground based units. Heavy bombers may be intercepted by AA batteries **, Fighters and Fighter Bombers. Heavy bombers cannot attack fighters or fighter bombers and may only defend against them.
Light Bombers receive the following bonuses: +50% against ground units, -15% to city defence per hit/attack and an additional +20% collateral damage. Both light and heavy bombers my attack the following: Tile improvements, cities, ships and all ground based units. Light bombers may be intercepted by AA batteries **, Fighters and Fighter Bombers. Light bombers cannot attack fighters or fighter bombers and may only defend against them.
Statistics (Heavy): Strength 18, Range 12, Cost 180 Hammers, Movement 1
Statistics (Light): Strength 15, Range 10, Cost 140 Hammers, Movement 1
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Other Considerations and Rule Suggestions
Variable Operational Range: I think the concept of a more detailed aircraft operational range would add a great deal of tactical and strategic options for the hardcore CIV IV gamer. In general, I would suggest that bombers possess the greatest range followed by torpedo bombers, then dive bombers and finally fighter bombers and last, fighters. In historical truth however some fighter aircraft possessed a very long operational range such as the American P-47 Mustang which had a huge fuel tank. While the Messerschmitt ME 109 fighter suffered from a short operational range although it was a formidable fighter in its own right. If specific historical WW II aircraft are used, these could have differing operational ranges reflecting this.
Repairs: Aircraft may “heal” on a carriers or military air bases simulating repairs and resting pilots. Both carriers and military air bases will be considered “friendly territory” for healing purposes.
Carriers should be able to hold 6 air units rather than only 4. Carriers should also be able to intercept all aircraft (30% chance), except light and heavy bombers.
* - A tile improvement that I think should be included in the game. The advantage is that they can be placed outside of the cities “fat cross” radius providing an earlier warning to impending attack and to be more able quickly respond to any enemy attack before any damage can be done to cities and/or tile improvements.
** - A WW II era unit that I think should be included in the game. Bonuses: +50% against all aircraft. Can only defend. 30% chance to intercept all aircraft. Statistics: Strength 24, Cost 80 Hammers, Movement 1.