As of Tuesday, nearly 22,000 of the 138,000 troops in Iraq were Marines.
The call-up will affect Marines in the Individual Ready Reserve, a segment of the reserves that consists mainly of those who have left active duty but still have time remaining on their eight-year military obligations.
Generally, Marines enlist for four years, then serve the other four years either in the regular Reserves, where they are paid and train periodically, or in the Individual Ready Reserve. Marines in the IRR are obligated to report only one day a year but can be involuntarily recalled to active duty.
To date, about 5,000 Army IRR soldiers have mobilized, and about 2,200 of those are currently serving, according to Lt. Col. Bryan Hilferty, an Army spokesman. Of those 2,200, about 16 percent are volunteers, he said. A typical Army enlistment obligation is also for eight years.
According to Stratton, there are about 59,000 Marines in the IRR, but the Corps has decided to exempt from the call-up those who are either in their first year or last year of the reserve status. As a result, the pool of available Marines is about 35,000.
The deployments can last up to two years, but on average would be 12 to 18 months, Stratton said. Each Marine who is being recalled will get five months to prepare before having to report.