Does the AI know the state of your defenses?

[SmartMuffin]

Just finished up a Noble-Pangea-Standard game in which something interesting happened.

Towards the end, only myself and the Spanish were left. I had a huge tech lead and my military completely dwarfed hers. Her army consisted of Cavalry, Artillery, and Infantry while I was running around churning out 2 modern armors and 2 mech infs per turn. I was going for Domination, and it was just a matter of time before I got her.

As I steamrolled through her territory, I noticed that she had a surprisingly large amount of these lower tech units to throw at me (I recall at least 7 cavalry being used to take out 1 mech inf). I dismissed it as Isabella being militaristic, so of course she'd have tons of units and attempt to put up a resistance.

So, as I was going through taking over, all of a sudden she lands three transports all full of cavalry (escorted by two battleships) on the other side of my land where the cities are still defended by longbowmen. D'oh! Obviously I made a dumb mistake forgetting to upgrade my defenses, but it got me wondering as to how exactly she knew that. Before the transports landed, she had no LOS to those cities. Had she kept those 20 cavalry around the front lines, they could have been useful.

So, to do an experiment, I reloaded to prepare for that exact contingency. I pumped out a couple battleships to make it harder for her transports to get through. I put at least two marines and one mech inf in each of my costal cities (and a modern armor in both to strike when they land).

Sure enough, the transports came again. So I guess the question is, what makes her decide to sacrifice a significant portion of her army to travel around the world (takes a good 5/6 turns) just on the HOPE that the other coastline won't be defended?

 

[Murky]

I think the AI has a tendency toward picking "low hanging fruit" or attacking where it thinks you are the weakest. It has become so common that I now anticipate some sort of surprise attack when they should be defending.

 

[Naismith]

Sure enough, the transports came again. So I guess the question is, what makes her decide to sacrifice a significant portion of her army to travel around the world (takes a good 5/6 turns) just on the HOPE that the other coastline won't be defended?

Short answer: The AI is stupid. You'd think they would send a caravel to gather intelligence before putting such a large effort into building an invasion force. After having seen similar behavior, I've learned to keep up my defenses in coastal cities even when an attack there would make absolutely no sense, and would be doomed to failure. Usually, they don't have adequate military units to keep the cities, even if they do manage to take one or two. They are landing an inferior military force right next to your biggest productions cities, which will churn out units fast enough to overwhelm them. It's just a suicide mission, but the AI doesn't grasp that.

But beware - if you have anything like military parity with an AI halfway around the world, they could build an invasion force that would be a real problem. Keep up your coastal defenses.

 

[MrCynical]

In Civ 4 the AI has no knowledge of your defenses that it shouldn't have by the game rules. If they can see your territory (remember at the late stage you were at in your game it is likely they have spies), they can see the state of your defenses. That said, the AI is inept at actually making use of that information.

 

[Glinka]

Can an enemy AI trade with a neutral that has complete view of all your civilization? Because if so, then the enemy could become aware of at least some aspects of your defense.

 

[Zanmato]

As far as I'm aware the only way of knowing the defenses of a rival's city is religion, having a LOS or using a spy. Map trading doesn't reveal such information. Isabella is stupid anyway and she did the same to me, but I quickly overwhelmed her 'pillage' party as that is all her invasion force came down to.

 

[nullspace]

I don't think this is cheating or stupid on the part of the AI. I'll bet that at some point in the past, Isabella had a caravel sail down your coast mapping it out, and noticed that your cities were lightly defended. Hundreds of years later, when you declared war on her, she used that old information to attack you where you were weakest, and it worked. When you reloaded and beefed up defenses, she didn't know that your defense had changed since she last saw it, and still attacked.

Actually, it's very impressive that a pathetic and backward AI forced you to reload in order to win.

 

[bkwrm79]

Even when it's just a pillaging party, I think it's often a wise move. And if you have defenses prepared, the AI's propensity for amphibious attacks has forced you to hold troops back defending your heartland and thus weakening your offensive. Either way, it helps the AI.

It can also be a real pain if you're trying to build a spaceship or something like that. The key is always to have a reserve.

 

[ChrTh]

My guess is that the AI is programmed to try a 'back-end' attack like that, correctly anticipating (in this case) that cities away from the front lines won't be as heavily defended.

In Civ 3, the AI always went after the least-defended city. As a result, a nice tactic to pull was to leave a city in the center of your empire undefended and pick off all the troops the AI sent towards it. I'm glad they fixed that.

 

[Naismith]

Even when it's just a pillaging party, I think it's often a wise move. And if you have defenses prepared, the AI's propensity for amphibious attacks has forced you to hold troops back defending your heartland and thus weakening your offensive. Either way, it helps the AI.

I see your point. However, I don't think it helps the AI to spend a significant amount of resources to build galleys, units, etc. that usually end up getting wiped out for little or no gain. Of course, this strat is usually not a wise one for the AI attacking you, but it does help any other AI's in the game.

It can also be a real pain if you're trying to build a spaceship or something like that. The key is always to have a reserve.

A reserve is the answer, at least partially made up of movement 2 units. At least enough to hold off an attack until (perhaps) stronger movement 1 units arrive. If you're building a spaceship, you should have already built an extensive railroad system, which should help immeasurably.

The fact is, if you've got a long coastline, you can't possibly fortify every city enough to resist a surprise invasion. Assuming military parity, and the occasional (accidental?) ability of the AI to concentrate forces, your only recourse is to build a fair number of ships, and place them out as sentinels so you can get a bit more warning that the invasion fleet is coming. If you have enough ships to actually sink most of the invasion fleet, that would be ideal.

 

[Palantir30]

In Civ 3, the AI always went after the least-defended city. As a result, a nice tactic to pull was to leave a city in the center of your empire undefended and pick off all the troops the AI sent towards it. I'm glad they fixed that.

Agreed. You could literally have a cheerleader-tunnel of Mech Infantry leading from a border to an undefended interior city, and the attacking army would walk down it toward the city, giving you several turns to bring artillery up on either side of the cheerleader tunnel before taking out the troops.

Lovely AI. I'd say the new AI is one of the few strategic game balance aspects IV has over III.

 

[Zebra 9]

It is most likly a preprogramed strategy. I know that when I go to war I always leave my rear in weakend state. I don't think that the rear assault is a wast because it is probobly premeditated and isint that what a navy is for, attacking the enemy's coast.

 

[SmartMuffin]

Actually, it's very impressive that a pathetic and backward AI forced you to reload in order to win.

Perhaps you didn't quite understand.

I won the game regularly. I nuked the transport to half the total HP of the invading force. She still took my one costal city, but as was pointed out by someone else earlier, it was right next to my two biggest production cities who quickly produced the necessary units to re-take said city.

I reloaded because I was curious. Not because I had to.

 

[nullspace]

OK, that's my mistake, I see the word "reload" and I start thinking "cheating", and it wasn't in this case.

But my main point was that it was a good move for the AI, and it didn't cheat at all to do it. If the war had been less one-sided, it might have made a difference. I think the AI does observe and remember where your defenses are weakest (unlike in Civ 3 where it always knew where all your troops are).

 

[SmartMuffin]

It was a good move originally.

But upon the reload, it was not a good move. Don't get me wrong, I like that the AI considers sneaky tricks like that, but I think it should be based on something. Unless there's some sort of "We're gonna lose anyway so let's just try something ridiculous" algorithim programmed into the AI that nobody knows about.

 

[cymru_man]

What, precisely, are you complaining about? You say the AI executes its planned invasion whether you sneakily improve the defences or not. That's good - surely if the AI magically found out you had improved your defences when it shouldn't do, then it would be clear it was using some information it shouldn't have.

 

[SmartMuffin]

It shouldn't magically find out.

But it should take some initiative to make sure that the invasion fleet which comprises nearly half of its overall military strength isn't walking right into a trap where it will be eliminated MUCH more quickly than if it stayed fortified at home.

No rational human would make an attack of that sort completely blind to the defenses that may await them. And at the same time, if those defenses did turn out to be strong, the invasion would then be cancelled. Not really a complaint, it's not a big deal, I'm just trying to figure out why the AI makes certain decisions...

 

[Harrier]

So, as I was going through taking over, all of a sudden she lands three transports all full of cavalry (escorted by two battleships) on the other side of my land where the cities are still defended by longbowmen.

As others have mentioned Civ3 in reply to this post - In Civ3 the AI would usually land ONE unit and then leave it immobile. At least Civ4 lands a lot of units and then uses them.

 

[SmartMuffin]

I dont remember much of Civ3.

I played it for about a month then sold it

 

[BadHorsie]

I think the AI has a tendency toward picking "low hanging fruit" or attacking where it thinks you are the weakest. It has become so common that I now anticipate some sort of surprise attack when they should be defending.

Yeah, if you're attacking on the other side of the map, ALWAYS prepare to defend you coastline on the opposite side where they will almost always launch a counter attack round the back.