I'm digging - right now I have the AA formula:

- The real strength of each AA unit is 1/10th of the value shown in the editor. So Flak has a strength of 0.2.
- Each AA unit in the tile being bombarded takes a shot against the defense of the bombarding air unit. The chance of shooting down the air unit is A/(A+D), as with all other forms of combat in Civ3. Remember, A is 10 times less than what is in the editor for the AA unit.
- The maximum number of AA units that are given a chance to shoot down the plane is 4. Any AA units above 4 are ignored.

So, for example, if you want the formula for the probability of N units with a strength of A shooting down a plane with defense of D, here it is:

1 - (D / (D+A))^min(N,4)

You can find a discussion

HERE.

That means by giving these air unit artillery pieces the max defense value the editor allows would minimize the odds of them being shot down when they shell tiles with AA units/improvements. By setting interception chance to 0% with stealth they won't shoot down fighters. They can still be bombing sponges though that with that high defense because air units can still lethally target them regardless of what ground unit guarding them (like aircrafts on an airfield/city). But with -4 HP I think it could be fair. Artillery pieces could get destroyed by airpower.

An air unit artillery piece with a defense strength of 50 and -4 HP would have a 3.2% chance of being shot down by a cluster of 4 Mobile SAMs with the AA value of 4 (0.4 entered into the combat calculator).

And a 7.4% chance of being shot down by a SAM Battery with Interception percentage set at 50%.

And a 28.8% chance of of being destroyed by a bomber with a bombard strength of 12 ROF:3 in the open where the bomber will target air units half of the time.

I'll start testing with these values. Even against the strongest concentration of AA the game could offer, there is a less than 10% chance of you losing the artillery piece while still allowing for bombers to hit and destroy them. They do cover the regular aircrafts from bombing runs though.

I still don't like how squishy the regular aircrafts are to being bombed. It's like air combat doesn't matter as much as trying to wipe them out on the ground. A bomber with 12 bombard strength, ROF:3 has a big chance of wiping out its grounded counter part/fighter with a defense value of 2 and 4 HPs.