Every airfield and carrier should have a set limit of resources. I.e. 50 - 500lb bombs. 20'000 rounds of MG ammo, 5000 rounds of MG ammo. 50000 gallons of fuel, and 50 pilots.
Every time you up an aircraft, tank, or take a seat in a AAA gun, you use up these resources. Similiar to rebuilding, each airfield gets resupplied by the convoys, barges, and trains.
I.e. if 10 P-51's up at airfield A17, they take up 15'000 rounds of MG ammo, 20 1000lb bombs, and droptanks for 4000 gallons of fuel and TEN pilots. The airfield supply count goes down for each amount. Some ups a formation of B-17 bombers with 8x1000 bombs, that 24 x 1000lb bombs, 19140 rounds of MG, 30 pilots, and 8430 gallons of fuel.
It places greater emphasis on the factories because by destroying them, it reduces the re-supplying times of the fields. It also might allow for more factory types, munitions, bombs, etc. Hit a train station, it lengthens resupplying. Hit and destory a vehicle convoy on the way to a field, it actually stops it's resupply.
By forcing more of a focus on the strategic targets, it gives a more dynamic feel to the gameplay. For example, hitting the fuel tanks at an airfield truely reduces the amount of fuel available. Hitting ordinance has the same effect of course, but it also includes MG and Cannon rounds. Hit barracks, it reduces the number of pilots available.
It also means that an airfield can run out of pilots, bombs, MG rounds, cannon rounds, and fuel.
You can also introduct a wider range of resupply options for an airfield. Instead of supplies, sending troops is actually sending pilots. You should have the option of resupplying fuel, A/C ammo, and bombs. Of course, we'll need the DEUCE truck added.

Thoughts?