How does Air Defense rating work?

[Fistleaf]

Let's say a Flak with air defense of 2 is bombarded by a bomber with bombardment of 12. Is the chance of bombardment success given by 12/(12+2)? If so, does bombardment of a transport with air defense of 0 always succeed?

[Solomwi]

No, the success of your bombing mission is determined by B/(B+D), where B is your unit's bombard strength and D is the targets defense rating (not AA). I believe the AA rating comes into play as an offensive rating against your unit's defense. IOW, success of an AA counterstrike is AA/(AA+D), roughly put. I'm just guessing on this part, but suspect that the AA rate also comes into play when determining whether or not an AA attack will happen, but that this is a separate RNG action from the success of the AA strike.

Waiting on Catt, vmxa or alexman to set me straight...

[Solomwi]

I'm correcting myself here, maybe. After looking around the editor a bit, I think the RNG action determining whether an AA unit hits back or not is the same 50% (5% for stealth) intercept chance that interceptors have had since the beginning, and is not dependent at all on AA rating.

[Fistleaf]

So is the AA rating used on counter-attack similar to the 8 attack by a SAM battery?

[Solomwi]

Yes, once it's determined that an AA attack will happen, it becomes AA rating vs. aircraft defense, AFAIK.

[Catt]

Originally posted by Solomwi
Waiting on Catt, vmxa or alexman to set me straight...

alexman solved it, but I can at least provide a link . . .

The Link

The main formula:

Originally posted by alexman
AA combat 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)

Catt