From the Summary: "This report provides a summary estimate of military forces that have reportedly been deployed to and subsequently withdrawn from the U.S. Central Command (USCENTCOM) Area of Responsibility (AOR), popularly called the Persian Gulf region, to support Operation Iraqi Freedom. For background information on the AOR, see [http://www.centcom.mil/aboutus/aor.htm]. Geographically, the USCENTCOM AOR stretches from the Horn of Africa to Central Asia. The information about military units that have been deployed and withdrawn is based on both official government public statements and estimates identified in selected news accounts. The statistics have been assembled from both Department of Defense (DOD) sources and open-source press reports. However, due to concerns about operational security, DOD is not routinely reporting the composition, size, or destination of units and military forces being deployed to the Persian Gulf. Consequently, not all has been officially confirmed."
CRS Report for Congress, RL31763