I once had a job which required that my productivity had to continually increase while a second major responsibility was to train new people who once they were prepared would directly compete with me and thereby make me less productive. The resulting experience was simply maddening. Trying to accomplish two directly contradictory tasks has a formal name, "Role Confusion". It is a personal nightmare and a serious management mistake.
Role Confusion is what our soldiers in Iraq are exposed to every day of their tour. We are asking them to take on an enemy in mortal combat and befriend, train and be sensitive to the needs of peaceful Iraqi civilians when there is no way in hell to tell the difference between enemies and non combatants.
When you add to this vile brew an overhang of being a target at every moment for invisible snipers and assassins with explosives, the result is a constantly high level of stress. The insufficient number of our men and women available has resulted in multiple tours of duty in which all of these stressors are replayed seemingly without end.
The casualties of this war therefore are not and will not be limited to those killed and those wounded. I can't be certain of course, but because of what I have described, the mental health casualties of those eventually returning from service will exceed, proportionately, similar casualties from Vietnam.