Defense officials say the study was done not because a pullout is about to be ordered but because basic decisions have to be made now for if and when that day ever comes.
The study assumes a pullout would occur under combat conditions, or, as one official put it, "the last guy out is a guy who can fight his way out."
Now retired and running a horse farm, Gus Pagonis commanded the pullout after the first war with Iraq — under much easier conditions.
"You're most vulnerable in any theater of operation when you're leaving," he told CBS News Pentagon correspondent David Martin. "There was no enemy threat, nothing at all. Now you're in a terrorist war-type activity where security will still have to be continued which will be a massive exercise."
There are 20 combat brigades in Iraq — each with about 50,000 tons of equipment. But that's less than half of what's there.
"You have hospitals, medical, ammunition depots, supply depots, water depots. They all have to come out and they have to come out in an orderly fashion," Pagonis said.
On top of that there are 129,000 private contractors working for the U.S. government. They all would have to come out on the same roads they went in on.
"There's not too many roads you can actually take a truck with a tank on," Pagonis said.
There were ambushes on those roads when American troops went in and the threat hasn't gone away.
"As soon as you park five or six vehicles, you're setting up a lucrative target for some car bombing or some kind of missile attack," Pagonis said.
The pullout would be faster if Jordan and Turkey allowed U.S forces to come through their territory. But defense officials say the critical factor is how much of the American military arsenal would be turned over to the Iraqis.
As for how much it would cost, no one has yet done the math.