From: Houston, TX
ORIGINAL: golden delicious
Not if the artillery is already at 1% supply.
In TOAW, good troops are still pretty effective at 1% supply. A lot of the time, the right play is to just bang away at everything and to hell with your supply level: what you want is to have your artillery fight for ten combat rounds on direct support, then be on passive support for the whole enemy turn, too.
1% supply does not mean out of supply. It just means maximum fire discipline has been reached. Obviously, infantry, tanks, and everything else besides artillery can directly apply their full strength throughout their player-turn, then defend throughout the enemy player-turn. Why should artillery be different? Whatever the supply model is applying to ground attackers, has to be applied to ranged support as well.
Let's look at the real world situation.
An artillery battery is supporting some attack somewhere, when a report radios in that there's a furious counterattack being made in the other direction and they're needed for counter-battery. The battery switches support halfway through its schedule to follow the new orders.
How on earth can the unit then be said to be fully supporting the attack? They cannot be bombarding both targets at once. Either they're dedicated to the attack or they're allowed to switch targets- which would be passive support.
Again, the only simultaneous movement TOAW supports is reserve movement. If reserve movement occurs, a directly supporting artillery unit will not switch to opportunity fire against it until its direct support orders have been completed. Again, the enemy player-turn is not occurring simultaneously with the friendly player-turn.