Probably to come home safe, right? If so, then why go in the first place? There has to be more to ask for than just that, like hatever reason for entering the armed forces. To protect something, but does God agree with what you are protecting, does God love America over the other countries?
What about winning? If they pray for winning, they are praying for God to support their killing of people (innocent and guilty, as is the case in war). Thay are also praying God likes us better than them, but I don't remember God creating people that he doesn't want to live?
Do they pray for the bombs to "do their job", and blow people up and destroy, etc...?
Does God grant wishes to those involved in a system of killing? If one single person of the side of America is not a Christian, then we are not the chosen people, how does that work? God would then have to support a non-Christain against a possible Christian on the other side. Perhaps Iraq is a bad example of that, since they are most likely Muslim on the "other side", but what about Vietnam, WWII, Korea, etc... where there was Christians on the 'other side'?
If God does grant these wishes, why for some and not others? And why do we have drag out wars that don't end? For some mysterious 'greater' cause? Like what? We still have war after all this praying, so what is the greater cause? Weeding out people, population control, seems a bit problematic to me, since God is supposed to 'give the gift of life' just to take it away?
Anything I am forgetting? If you can justify any of this, then you must be in the mind of God, because the word does not support any of this.
So why pray? Their guns protect them better than God can.