December26, 2006: The U.S. Army has noted that troops going back to Iraq for their second or third tour, are more likely to suffer from combat fatigue (or PTSD, post-traumatic stress disorder). Currently, about 400 soldiers a year are sent home from Iraq because of severe PTSD, and thousands have less serious bouts of PTSD, which are treated in Iraq, with the soldier soon returning to duty.

What the army is up against is something they discovered during World War II. Back then, PTSD was just called combat fatigue, and it was discovered that few soldiers went more than 200 days in combat without suffering a severe case of it. Actually, the number of days a soldier could survive in combat, before feeling the effects of PTSD varied from 100-200. There were exceptions, as PTSD vulnerability, like everything else, occurred according to a bell-shaped curve. There were some troops who had severe anxiety attacks, and other PTSD symptoms after only a week or two of combat. On the other extreme, there were men who never seemed to suffer any PTSD symptoms.

PTSD was less of a problem during World War II, Korea and Vietnam, because troops tended to get badly wounded and killed before they hit the 200 day mark. Casualties were very high in these previous wars, with some infantry units suffering one hundred percent casualties after only three months of combat. This calculation left out the days a unit was out of combat, something commanders tried to do as much as possible, to give the troops some rest.

By the end of World War II, there were some army combat units that had suffered over 200 percent casualties, and spent over eight months in combat. Note that "200 percent casualties" meant that the number of killed, wounded and captured equaled twice the number of people in the unit (usually a regiment or division.) The record for number of days in combat for a U.S. division is held by the 2nd Infantry Division, with 305. Interestingly, no Marine, or army parachute, division even came close to that. These "assault units" were pulled out of action after shorter, but more intense, periods of combat.

Thus, the average soldier can be effective for about 200 days of combat. After that, you generally have a case of serious combat fatigue; and someone dangerous to themselves and those around them. At that point, these veterans were best removed to non-combat jobs or discharged. In Iraq and Afghanistan, the army has found ways to delay the onset of PTSD by providing better living conditions, and equipment that makes combat less dangerous. The army also provides some leave time during the tour, which allows the soldiers some time outside of Iraq, and even a visit with his family back home. All this has increased the number of combat days a soldier can tolerate, before no longer being fit for combat.

During the 1970s and 80s (the "Troubles" in Northern Ireland) the Brits found that most troops had no difficulty handling two year long tours in Northern Ireland, within a couple of years. But three tours resulted in lower re-enlistment rates, increased instances of disciplinary problems, and a general rise in PTSD.

The bottom line is that the stress of combat has a cumulative psychological effect on soldiers. Today, after about 300 days of action, it's time to put that soldier into a non-combat job. This was actually done during World War II and Korea, although informally. Of the 650,000 soldiers who have been to Iraq or Afghanistan since 2001, 26 percent have served more than one tour. Since most soldiers sent to Iraq are on their first enlistment, they (or at least about half of them) get out after that one four year contract. Those that re-enlist are usually promoted to NCO rank (sergeant). These are the ones who will be at greatest risk, as normally they would rise through the ranks (team leader, squad leader, platoon sergeant) of a combat unit. It can take ten years to reach the rank of platoon sergeant, but if this is done with combat tours every other year (and assume 150 days of combat per tour), it's not going to work. The army wants to give the troops 2-3 years between combat tours, but there are not enough combat brigades to do that at current force levels in Iraq and Afghanistan. Thus the army will have to be increased in size, or the number of troops reduced in Iraq and Afghanistan. The army believes that if there are 2-3 years between combat tours, some of the bad effects of combat can wear off. But this is unknown territory, and it will be years before it is known if this approach will work.