AI criteria for attacking armies

[kinglyam]

I've seen in a number of instances on this forum people claiming that the AI won't attack your armies unless they really need the square, because it does a unit-by-unit comparison of odds instead of considering sending multiple units to do the job. I decided to put this to the test in my current game by sending an old army of 3 knights out during an era of riflemen to pillage the roads around my enemy's capitol.

They ignored me for a while, except popping off a cannon round at me from the capitol. Once they whittled me down to about half my HP, they sent a guerrilla after the army. The guerrilla redlined the army, and the AI finished it off with a ME.

All well and good, you say. The AI had enough brains to whack me a bit with a cannon until it thought it had a decent chance of offing me with a guerrilla. Bad guess on it's part, but they eventually got me. HOWEVER, the same turn, the AI decided to try attacking my army of four Sipahi. Which was sitting on a mountain. And was still green with HP. And, of course, they got whupped.

Does anyone know what calculations the AI go into before deciding to attack an army? The mountain I held was of only slight strategic importance...the AI could have gone around me to get where they wanted to go. For some reason, they decided to try going through me. Did they just get uppity after taking out my old knight army?

 

[Theoden]

If they desperately need a square they will always attack. Else, I think they want around 25% chance of winning to attack.

 

[catchsomezzz]

Most of the time, those cannon attacks are "auto-bombardments" - that is, fortified units with defensive bombard abilities including archers, bowmens, etc. can take a free shots at passing unfriendly units.

Otherwise, Theoden is right, AI Civs do not attack straight on at an army unless they have a 20-25% chance of winning on a unit-to-unit comparison. When you test this out, you can check with the Combat Calculator to verify.

The two exceptions I can recall off-hand are:

1. They really want (or to disconnect) that square because it has an important resource, luxury, or is a city they want to take (back).

2. After the discovery of flight, the AI goes crazy buiding bombers - and they'll bomb anything that moves in their range. So, when your army is severely injured by the bombing and their single units have a decent odd of winning, you'll see them attacking your army.

 

[Tomoyo]

If your army is the only unit on the AI continent that is not belonging to that AI, it will attack. If there is even a worker of another AI on that continent, not at war, I don't think it will attack the army.

 

[vmxa]

I do not see anything incongurant with the know facts. That is to say that the AI will not attack a green army in the field. Will rarely attack a yellow and always attack a red.

Being in the field or in the open is the key here. If you insist upon parking an army next to a city, then you are asking for bombardment. If you get some and it damages the army, it will get attacked. This is entirely consistent with what is reported by players that use armies a lot.

Stick any army in a city and even any number of armies in the city on an invasion beachhead and you will get attacked.

I have used inferior armies to pillage civs on sid level many times and they leave the army alone, even with hndreds of units available. Let that army attack and take damage and that is a different story. Plant a city and move the army in the city and it will get attacked.

You can use SirPlebs tactic of lining up a corridor of death in front of a city with one opening and the ai will march unit after unit down the line and take ZoC shots and not attack.

Now these tactics are risky once Flight comes along as bombers can reline armies or even kill them. You do not have to sweat arties units aas they are rarely used on attack. I have only once seen it and the civs was only passing through, so I am not sure it was an attack attempt (I killed that stack anyway).

Note that mods do not have to follow this concept.

 

[catchsomezzz]

Ah, "Zone of Control" - that's the word I was looking for. Thanks vmxa!

 

[kinglyam]

I do not see anything incongurant with the know facts. That is to say that the AI will not attack a green army in the field. Will rarely attack a yellow and always attack a red.

The knight army, sure, I understand why they did that. It's the Sipahi army I don't understand. It was green on a mountain, with space around it, and they attacked (I think with a guerrilla, which equates to less than a 3% chance of victory). The only reason I can think they would do that is they didn't like it sitting next to their city, but it wasn't a choke point. Guess I don't understand the "mind" of my opponent

 

[vmxa]

As to sending a guerilla, they will send any unit with attack flag, so it is not a surprise. You see them send a calv with 1 HP against tanks all the time. I doubt they figured it was a winning play. They just knew there was a unit in range and hit it.

As to Sip army, is this a modded game? I have had literally hundreds of armies and never had a green one attack in the open field. Is it one of the scenarios? I try to avoid ending my turn next to a city as that will often provoke an attack.

To me in the field or open field means not in an adjacent tile to a city or barricade.

 

[kinglyam]

As to Sip army, is this a modded game? I have had literally hundreds of armies and never had a green one attack in the open field. Is it one of the scenarios? I try to avoid ending my turn next to a city as that will often provoke an attack.

To me in the field or open field means not in an adjacent tile to a city or barricade.

Oh, sorry, I'm still new to the forums, and forgot the etiquette. I'm playing unmodded PTW (basically, got Gold and haven't done anything to mod it)

I see the difference here...when you said "open field", I thought anything outside a city is open. This army is next to one of their cities, so I guess they panicked and went after it. Hey, if they want to keep throwing units against it, it makes less I have to redline with my arty

 

[gskyes]

I'm just wondering, what would happen if you had a 12hp army with 3 veteran warriors (this is hypothetical, of course, nobody would actually build an army of warriors). Let's assume we are using C3C, unmodded game, and the army is completely healthy. Now you send the army into enemy territory to pillage some squares. When would the AI attack? Would it use a knight, a calvary, a tank, or a modern armor? Or would it not attack it at all?

I was under the impression that the AI will not attack an army unless it was wounded, in a city, or on a REALLY important square. But there must be a limit. That's why I came up with the rather extreme situation as a question.

 

[catchsomezzz]

Hmm, this has a study written all over it.

"AI criteria for attacking armies" by your name here

So, any takers?

 

[Doc Tsiolkovski]

I'm just wondering, what would happen if you had a 12hp army with 3 veteran warriors (this is hypothetical, of course, nobody would actually build an army of warriors). Let's assume we are using C3C, unmodded game, and the army is completely healthy. Now you send the army into enemy territory to pillage some squares. When would the AI attack? Would it use a knight, a calvary, a tank, or a modern armor? Or would it not attack it at all?

I was under the impression that the AI will not attack an army unless it was wounded, in a city, or on a REALLY important square. But there must be a limit. That's why I came up with the rather extreme situation as a question.

Nobody would build a Warrior Army, but everyone would build a MW (or even Horsemen) Army...
It really isn't that mysterious. Just consider "Strength" (=HP * A/D value).
So, a Warrior Army is 12*1=12 on defence, and that equals a vet Sword attacking...
The AI will not hesitate to attack on flat ground. I can't tell for sure if the Army is safe from Swords on Mountians, but I know it isn't safe from MDI.

Knight/Cav Armies in the open won't get attacked before Tanks or Marines.
Army is 12*3=36, Marine is 4*12=48. Cav/Inf/Guer is 4*6=24, no surprise they don't attack.

This shows us that the Army Immunity in unmodded largely attributes to the huge gap in attack strength: It's a long time from 6 (Cavs/Inf/Guir) to 16 for the Tank/12 for Marines.
I can tell for sure that this immunity is not so total in mods.

Just to clarify one thing: The AI will not start a real attack on an Army next to a city. But, the AI is programmed to make a suicide attack against a besieging stack (you often see those Longbows earlier). So, they'll throw only one unit against the Army.
Of course, if they're lucky, the AI drops enough in HPs to become a target for elimination...

Also, Airfields/Radar Towers aren't safe; they'll get attacked just like cities defended by Armies.

 

[vmxa]

Al I can say is that I have not made a warrior army, but I have made a sword army. No army I have ever had has been attacked in the open, while healthy by the AI. That is to say, not next to a city and all HP.

This includes Knights and Calv armies while tanks existed. I cannot say how many armies I have had, but the most leaders I can recall in a single game was 55. Twenty or more armies is quite common in my sid games as I will immediately make an army with any leader before fighting further. I will keep the MA city making armies non stop, if I have enough cities to permit it.

I will admit that I do not tend to leave armies sitting in the field all that much. I remember a Demi game having a Galic sword army last the whole game and using them to cover other units and they were not attacked. I cannot say what opportunities the AI had.

I can also say that when invading, I always drop off a stack and it is not attacked, if it has armies in it, regardless of what the AI has (pre flight). The moment I found a city with that stack in the city, it comes under attack. They will send troops, even if they are inferior.

IOW I see horses, archer, tanks, any unit with offense flag on. So I am not convinced it see any winning odds, it just comes.