"..The “transitional force” he will leave behind will no longer participate in major combat missions but instead train and advise Iraqi security forces, hunt down terrorist cells and protect American civilian and military personnel working in Iraq.."
...and more on the Logistical Nightmare, here from Global Policy Forum.
"...Even with the benefit of a detailed plan, Payne said, "this is going to be an enormous challenge." Extricating combat forces during an active war is a tricky military maneuver under the best of circumstances, according to interviews with senior military officers and dozens of tactical and strategic military planners and logistics experts in Iraq and at U.S. military facilities across the region. A hastier departure could find military convoys stalled on roads cratered by roadside bombs, interrupted by blown bridges and clogged with fleeing refugees; heavy cargo planes jammed with troops could labor into skies dark with smoke rising from abandoned American bases..."