WASHINGTON - For years, US military planners have worried about the risks of maintaining a large force in Iraq. Now, they are worrying about how to get it out.
In what is shaping up to be the biggest logistical challenge since the Vietnam War, the Pentagon is grappling with how to transfer out what a top official calls "mountains of equipment,'' along with 143,000 troops and a similar number of civilians, amid the continuing threat of roadside bombs, ambushes, and suicide attacks from insurgents and terrorists.
There are worries, too, that arms will fall into the wrong hands, or that the complex withdrawal will drain resources needed for the buildup of the war effort in Afghanistan.
Concerns about the difficulty of the endeavor, which is set to be in full swing next year, have prompted a flurry of new government reviews and closed-door briefings for members of Congress who believe the process needs greater oversight.
Top officials say a big focus of the planning is ensuring adequate protection from a possible spike in attacks with improvised explosive devices - or IEDs - as troops pull out of relatively secure, fortified bases.
"We anticipate [attacks] possibly going up as we start moving these large units and convoys,'' Army Major General Kenneth S. Dowd, the director of logistics for the US Central Command, said last week by telephone from Kuwait, where he was huddling with the logistics chiefs of each branch of the military. "If that keys up again we may have to slow down.''
President Obama has set a timetable of removing the bulk of US forces by the middle of next year, and the rest by the end of 2011. A recent internal Army report laid out the sheer enormity of the task: 31 million items must be moved, including 100,000 pieces of "rolling stock,'' 120,000 containers, 34,000 tons of ammunition, and 618 aircraft. The job will require an estimated 240,000 truckloads, which translates to 8,000 convoys. Much of that material will contribute to 119 shiploads. Nearly 300,000 American personnel, military and civilian, will withdraw, and 350 bases large and small across the country will be shuttered or handed over to Iraqi forces.
At the Pentagon, top officials are working overtime to manage the process.
"When you get down in the boiler room and look at moving mountains of equipment that is accumulated over six years of war in Iraq and either bringing it home, or donating it to the Iraqi security forces, or taking it to Afghanistan, it is a huge logistical challenge,'' Ashton B. Carter, the undersecretary of defense for acquisition, technology, and logistics, said in a recent interview.
Carter, who recently traveled to Iraq and Afghanistan to see the logistics effort firsthand, added: "We need to do all this as we complete the mission and make sure there is still stability in Iraq.''
US military officials are identifying what types of equipment, such as Humvees, could be donated or sold to the Iraqi Security Forces, Dowd said. But there is the question of what to do with the rest.
The most sensitive items, such as intelligence gear, will be flown out of the country. A major challenge remains identifying the safest and most effective ground routes for the bulk of the supplies, most likely through neighboring Jordan and Kuwait, where a large share of the equipment will be loaded onto ships for ultimate transport to the United States or Afghanistan.
Meanwhile, in addition to the primary travel routes, military planners are also identifying backup routes in case of disruptions, officials said.
Another major task will be to keep track of everything in transit - a notorious failure after the 1991 Persian Gulf War when the Pentagon had thousands of containers sitting in Kuwait but had no idea what was in them.
"One of the biggest challenges,'' Dowd said, is "accountability and [knowing] what's in the containers.''
Unlike the first war in Iraq, when hostilities ended with a cease-fire, there are still armed groups attacking US and Iraqi troops so there is a higher risk in losing track of weapons, said retired General Jack Keane, a former Army vice chief of staff who is now a partner at SCP Partners, an investment company.
"There is an obligation to know what we have, where it is, and where it winds up,'' Keane said.
There are also environmental concerns about abandoning hundreds of bases and camps that have been established since 2003.
Dowd said environmental experts have begun assessments of the first group of bases that will be abandoned or handed over to the Iraqis to ensure they are cleaned up.
All this is drawing increasing scrutiny from government auditors and congressional oversight committees. A team from the Government Accountability Office was in Iraq reviewing the situation last week, while the House Of Representatives recently passed legislation requiring the Pentagon to provide periodic reports on the progress of the effort.
One pressing concern is that the withdrawal from Iraq could at least temporarily deprive the war effort in Afghanistan - and possibly other military missions - of critical resources, such as cargo planes, ships, logistics personnel, and security teams.
"The redeployment of forces and equipment is an enormous undertaking which will affect Iraq and the countries in the region, and which will also affect the ability of the US to conduct war in Afghanistan and be ready to respond to other threats,'' Representative Ike Skelton, a Missouri Democrat and chairman of the Armed Services Committee, said in a statement last week after receiving a classified Pentagon briefing on the redeployment.
Skelton said he also worries about too much equipment being left behind. He cited the Vietnam experience as a cautionary tale. "When I visited Vietnam years later,'' he said, "I remember seeing rows and rows of US equipment that we left behind. We must do a better job managing the redeployment from Iraq.''