U.S. Army efforts to insure that as many soldiers as possible serve overseas, are succeeding. Currently, 13 percent of the 500,000 active duty troops have never been to Iraq or Afghanistan. Two years ago, it was 42 percent, a year ago, 32 percent of soldiers had avoided combat tours.
Meanwhile 20 percent have been there more than once. In some job categories, like Special Forces, troops had spent more than half the previous five years in places like Iraq and Afghanistan. While the army also has some 600,000 reservists, they also have legal restrictions on how much they can be activated. And for morale (and recruiting) purposes, you don't want to send them into harm's (or discomfort's) way too often.
There were also some serious problems with getting that number down to zero. For example, there are always some members of the active duty army who, for various reason (health, pregnancy, or a rare job skill), cannot be sent to a combat zone. But that still left plenty of troops who had not been overseas, but could be sent. In some cases, that would be done by having more civilians take over jobs done stateside by troops, and make more troops available for combat zone jobs.
The U.S. Army is planning for the possibility that it may have to keep about 100,000 troops in Iraq through 2010. It also wants to send troops to "overseas hardship posts" (like Iraq, Korea or Afghanistan) only once every three years. In theory, that should be possible. There are some 150,000 troops in those hardship (where you can't take your family, and are likely to be shot at) assignments, and 570,000 active duty troops (plus over half a million reservists who can be called up for a year every few years).
Another solution is to allow families to go with the troops to Korea. This is being introduced. With fewer troops in Iraq, and not as many planned for Afghanistan, the army many not get everyone to a combat zone because there are not enough people needed in those places.