The U.S. Air Force is switching from four month to six month tours of duty in combat zones. This saves money on transportation costs, and means fewer units have to be sent overseas. The air force also knows that the stress of a six month tour is not appreciably greater than for a four month one. The air force will phase in the new policy over the next year, first increasing tours to five months, then six.
The British were the first to note that six months was the optimal length for combat tours. The U.S. Marine Corps also adopted the six month tour. The U.S. Army is under increasing pressure to use six month combat tours, rather than the twelve month ones it has been using for over half a century. This issue has come up increasingly over the past three years. For example, the army noticed that the emergency 15 month tours used for the 2007 Surge Offensive in Iraq led to much higher rates of PTSD and noticeably lower morale. The army has been aware of a "tour length problem" for some time. Four years ago, the army again seriously considered the use of shorter combat tours in Iraq and Afghanistan, largely because of the Internet buzz from troops who had been in touch with marines and air force personnel who already enjoy 4-6 month tours. But the brass decided against any change.
Six years ago the army considered, and decided against, reducing 12 month tour of duty in places like Afghanistan and Iraq, to six or seven months. Then, and now, there were two main reasons for not having shorter tours. First, the army units are the most heavily involved in reconstruction and peacekeeping. This involves direct contact with locals and it takes time to build relationships. New units coming in take a month or so to get tight with the local relationships the units before them had built up, and are passing on. So if you cut the tour to six months, you have less time in country with all your local connections tight.
The second problem has to do with the special training units go through before they are sent overseas. This would be the same for a twelve or six month tour. Actually, National Guard and reserve units go through more training than active duty troops, and would suffer even more from the shorter tours.
The impetus for even considering a change has come from the troops themselves, via the Internet. Over the last six years, many soldiers and marines (both officers and enlisted) have been comparing notes. Not just via email, but often face-to-face while in Iraq or back in the states. The Internet has made it easier for soldiers and marines to get connected. Another factor is the greater respect the marines have for soldiers. Since World War II, the marines saw themselves as elite volunteers, obviously superior to all those reluctant draftees in the army. There was some truth to this, but that has changed since the army went all volunteer in the 1970s, and especially since the army developed exceptional new training methods two decades ago. First in the 1991 Gulf War, than in Afghanistan and Iraq, the marines could see that the soldiers were not just volunteers, but pretty professional and bad ass. This made it easier for troops from the two services to compare their experiences and exchange combat tips.
One of the comparisons involved the seven month and twelve month tours. Bottom line was that, while there were hassles with the shorter tour, it was much better in the mental health, and domestic tranquility departments. Even if soldiers and marines did the same number of months in Iraq, the consensus was that it was easier to handle six or seven months at a time. Wives and kids liked it better as well, which is a big deal since over half the troops are married. A third factor has to do with the "no booze" policy in combat zones. While many guys can unwind with Xbox and a Marlboro, others really need a few beers. Twelve months, even if broken up by one or two short vacations, is a long time to go without an occasional drink.
As a result of experience during the 2007 "surge" in Iraq, the army has decided there will be no more 15 month tours unless there is a dire emergency. But there won't be six month tours either, not just yet. First the army wants to give the troops more time at home between 12 month tours. Some officers, however, are urging that there at least be some experimentation with six month tours, to see to what degree morale, and re-enlistments increase.