IMO the notion of the zones, etc is good, but needs tweaking. Cities should be the base origin of supplies, with factories being next. So cities can resupply factories, and factories resupply bases.
Get rid of the "resupply convoy every 15 minutes irrespective of route length" thing.
Have supplies automagically trickle down the supply chain at a rate dependent on the amount of damage to the supplier, but make it fairly slow. ANd ensure that if the chain of supply is broken, then bases WILL "wither on the vine" unless resupplied by player efforts.
Options for AI resupply convoys:
1. have them as extra dollops of supply, over and above the automagically supplied. If the foe kills a convoy, the bomus supplies dont get through
2. or the convoys could have no effect on resupply at all if left untouched, but could halt automagic supplies for a defined period if destroyed.
Resupply convoys should go at real-world speeds. Truck convoys could have fairly small but frequent effects on resupply, whereas barges or ships could have larger effects, but less often, and trains would be bigger and faster than trucks convoys, but less frequent.
Automagic resupplies should not be adequate to keep a side going full throttle all the time; normal use at front line bases should deplete stocks of fuel and ammo (at least), and possibly affect availablity of vehicles.
That way, there is a point to defending friendly supply convoys (particularly shipping ones, which could give a large boost to an area for a long while) and for finding and attacking enemy ones.
And because teh automagically delivered supplies are not really enough to support normal ops, it also encourages more player flown/driven supply runs, too. Making the automagic resupply go at a low rate would also mean that newly captured bases were not so easy to operate from at full force, and give players real headaches about outrunning their supplies in advances.
Making supply convoys move at more realistic speeds and encouraging people to fight over them might mean we get to see the things in-game more often, too - Can't recall the last time I've seen a train in an online arena. Having road and rail networs criss-crossing the terrain means that GVs have things to fight over aside from bases. They could try to throttle supply chains.
Ooh, final suggestion: allow suitable bases to be able to launch a player-controlled supply convoy. Such convoys to have player-mannable gun positions (MGs on trucks, that and light AA on trains and barges - the usual on ships). All follow normal AI resupply convoy routes (although perhaps players might be able to pick a route out of a small selection), except for supply ships, which are player controlled as per normal convoys. And woe-betide anyone daft enough to send an ungaurded ship supply convoy into dangerous waters... the idea here being that other players would command armed fleets to guard the supply fleets.
DD fleets would have a purpose aside from helping out CV fleets with AAA, too.. and make the 3-4 inch guns on DDs mannable, and they could help with a little shore bombardment, or even go raiding. Hmmn.. make em trios of DDs (a bit like buffs) with a limited supply of torpedos (only resuppliable from a port), too...
:-}
Damn, I'm good at thinking of work for others to do! :-}}
Esme