The U.S. military knows it has a problem with multiple tours (of from 4-15 months) in combat zones. It turns out that this has been more of a strain on enlisted personnel. While officers also do multiple tours, the number is usually less, as they are often rotated to schools, staffs, etc. The enlisted personnel, especially the career NCOs, keep going back to war, and this is putting more stress on the NCOs.
The army is eager to hang onto experienced combat NCOs. When NCOs began leaving the military in greater numbers, the first response was to offer more money/ Two years ago, the U.S. Army introduced a "warrior pay" bonus plan that paid more money based on rank, and the amount of time one has already spent in combat. At that time, combat pay was $225 a month. In addition, all your pay, for time spent in combat, is not taxable. Previously, everyone, regardless of rank or length of service, got the same $225. The new rules increased the combat pay depending on rank, and previous time spent in combat, thus the Warrior Pay plan could increase this as high as $740 a month. This new system was meant to help keep the most experienced combat leaders in service, and provide a bonus that recognizes that value in a tangible form. This system tried to deal with the fact that the war on terror will be a long one, that was requiring many career NCOs to spend a lot of time in combat zones.
But the army and marines are also seeing an in increase in psychological stress problems because of multiple combat tours. It�s been 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). At the peak of the fighting, in 2006-7, about 400 soldiers a year were 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, on average, 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 not a catastrophic 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 earlier 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, so they could prepare for their next operation.
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. This was an unofficial policy ever since World War II. Experienced commanders didn't need a shrink to see that a guy had the "thousand yard stare" and other symptoms of someone too much combat stress. It was easier to get the guy a transfer, than to go through all kinds of red tape and hassle with the medical community.
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 casualty rate is the lowest in history (less than half of what it was in Vietnam). 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. But now the army is sending a huge number of troops into combat for unprecedented amounts of time. This sort of thing has happened before, because so many soldiers are surviving combat and piling up the days in action.
This has happened before. 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. There was not a lot of shooting in Northern Ireland duty, but there was a lot of stress as troops patrolled hostile neighborhoods. 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 worked during World War II and Korea, although informally.
Of the 800,000 soldiers who have been to Iraq or Afghanistan since 2001, about a quarter of them 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 often 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, and with the defeat of the Sunni terrorists in Iraq last year, there are now enough combat brigades to give the troops a longer break before going back. 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. At the moment, it's possible that the army and marines will not end up with thousands of combat experienced NCOs, but instead, will have many of those NCOs not psychologically fit for combat duty. So far, the permanent PTSD losses are less than half the combat deaths. But PTSD is a long term condition, and the number of these casualties may increase over time.