I've noticed that when I have two similar units promoting, and I promote one with the extra first strike promotion (drill I promotion), and the other with the extra 10% (combat I promotion) when attacking, that in future battles the one with the first strike promotion has a lower percentage for winning a battle than the one with the combat I promotion. So what's going on, and when would you want to promote units for extra strikes? It appears to be a weaker promotion.

Another question on first strikes -- take the Cho-Ko-Nu unit, which has an extra 1st strike and also causes collateral damage. Does that extra first strike result on average in more collateral damage? What if you've promoted this unit several times with Drill II and drill III, and the unit now has numerous 1st strikes -- for giving collateral damage is this better than promotions of combat I, II, and III promotions, or should it end up being about the same?

Thanks in advance for your answers...

First strikes are better when you're more powerful than what you're attacking. They allow your unit to fnish off the enemy without even taking damage because the enemy is dead before the first strikes are up.

This is situational, but it does have it's uses. It's great for ships because each new ship technology is such a big boost to the previous. Privateers with first strikes can take out large amounts of triremes and galleys of tech backwards civs without taking damage themselves.

Drill 1 is weak, but once you get to drill 4 you have so many first strikes you can take out multiple weaker enemies without ever taking damage.

Another situation where you might see this effect is with defenders that have been weakened by siege.

If you want to see the power of drill play a game as Ethiopia or America. Drill 4 Seals get a ridiculous amounts of first strikes. They'll take out fighter weakened infantry without ever taking a scratch, and your entire force will always be at full health (though march helps too). Oromo Warriors already start with drill I and II, so with theocracy you can get Drill IV from the beginning. Same deal, they'll take out the enemy's longbows and stay at mostly full health and only your trebs/cannons will ever take damage.

This might help http://www.civfanatics.com/civ4/strategy/combat_explained.php

there have been a couple of discussions about this, this article, Combat Explained, and this thread here specifically go into some detail about how combat and various promotions, including drill, work.

Barrage is the only promotion that boosts collateral damage.

Higher ranks of Drill can also be useful for city defenders, but I'm more prone to choose City Garrison and then get Drill as needed.

Drill II and III are pretty decent. Drill IV is awesome. Drill I is horrible, which hurts the other promotions because you need to "waste" a promotion on Drill I first. The strength of Drill IV makes for the crappiness of Drill I, but only your elite units will get promoted that far.

What also sucks is the units that are immune to first strikes. Makes a situational promotion even more situational.

I could write more on Drill, but it's a topic I've beaten to death and don't have the patience right now. I might add more later.

Drill is good for protective civs, since you have the "waste" DI promotion already behind you for free.
Drill also indirectly increases the amount of experience you get from combat since a DIV gives you 3-6 first strikes, which are an important combat advantage. If you attack with a DIV frigate a stock one, the strength ratio is 8 vs. 8. It means that you still deserve 4xp, even though you are going to have a +/-85% win chance. Whereas a CIV upgrade would give you a similar victory chance, but the strength ratio would 11,2 vs 8 would give you a 2.8571 xp factor, rounded down it would result in getting 2 xp from the same victory chance.

interesting is that when you want to have combat %s as high as possible, even with protective its better to go combat promotion.. ;)