For the third time since the Vietnam war, the U.S. Army is trying to go back to a form of organization that has been successful for several thousand years. Put simply, the army plans to assign soldiers to a unit, where they will stay, with few exceptions, for their entire career. This is sometimes called the "regimental" system, in recognition of the custom of soldiers before World War II joining a specific army regiment, and staying with it for as long as they were in the service. This was largely abandoned during World War II when the army came up with the "Individual Replacement System" (IRS), where individual soldiers were considered parts of a machine and replaced individually. This never worked, especially in combat, because the new replacements didn't have a chance to be integrated into the unit. After World War II, the IRS went wild, shifting troops around constantly. Instead of sending units overseas for a tour of duty, individuals were sent, insuring that the units overseas, and in the United States, were always full of people trying to get to know the people in their unit and their jobs there. The two earlier attempts to eliminate IRS failed because the army didnt recognize that you had to keep officers, as well as the troops, in the unit for long periods of time. Earlier efforts concentrated on the troops staying put, but kept moving the officers around. Since World War II, army officers have come to believe that their best chance for career advancement was to move to a new assignment every three years. This does not work if you are trying to create well trained and led combat units. This time around, the idea is to keep everyone frozen in a unit for at least 18-24 months (or more) at a time, as the unit goes through a year long training cycle, and is then tested for combat readiness, and sent overseas, or kept in readiness in the U.S., as a combat ready unit. After that, troops can be transferred for schools or new jobs that dont exist in the unit. Since most enlisted troops enter the service for at least three years, many of them would leave as well. Most enlisted troops stay for only one enlistment. The unit would then go through the cycle again. If there were an emergency that required more units than were ready, those that were still in training could be sent with the understanding that they were not as qualified for combat as units that had finished their training.