I think the almost limitless fun of fighting over an airfield would be perfected if when the last grunt walks into the maproom, the field doesn't immediately get all ack up and firing instantaneously. Have one random gun start working, then randomly add another for every minute that passes.
This way, fights over fields can ebb and flow a bit more. The capturing team can drop more troops or supplies to rebuild ack faster.
That's for auto ack. Player-manned ack should be available from the moment the field is captured.