President Obama confirmed on Oct. 21 that the remaining 39,000 U.S. troops will leave Iraq at the year's end. The war may be ending, but the size of the U.S. embassy in Iraq will  double, from approximately 8,000 to 16,000 people.

This is uncharted territory for the State Department; it has never managed a mission this size before. The Obama administration is requesting $3.2 billion to cover the transition from civilian to military control, in addition to a core operational budget of $496 million. The embassy in Baghdad is a sprawling fortress, the largest the U.S. has ever built. Three provincial posts in Basrah, Erbil and Kirkuk will extend the U.S.'s diplomatic reach into northern and southern Iraq.

But roughly ten percent of this team will actually include diplomats. In addition to their traditional work, the State Department will assume over 300 activities that the U.S. military routinely performs, including air transport, force protection, medical aid and environmental cleanup.

They will  require an extraordinary amount of contractor support.  Inside the embassy will be the newly established Office of Security Cooperation that will be responsible for Pentagon assistance programs to the Iraqi security forces; it will include more than 900 civilians and uniformed military personnel, in addition to 3,500 contractors. A  "general life support" team of about 4,500 employees will also cook, clean and run the embassy facilities.

And 5,000 security contract employees will protect the roughly 1,700 American diplomats as they attempt to pursue U.S. policy and development goals in an immensely complex country where two explosions in a Shiite neighborhood in eastern Baghdad killed 17 civilians on Oct. 13,  Turkish troops are fighting the Kurdistan Workers' Party in the north, and an eager Iran watches from the east.

All of this adds up to a new experiment in U.S. statecraft.  Whether this civilian-run operation is too bloated, on target or under-resourced remains to be seen -- but its successes and failures will help steer U.S. post-conflict strategies for decades to come.

(Katherine Brown is on the staff of Bloomberg View.)