At a US base south of Baghdad, trucks plod in either direction amid a hive of activity: with the clock ticking on a year-end withdrawal from Iraq, preparations are in full swing.

Located in the centre of Iraq, just 50 kilometres (30 miles) south of the capital near the town of Iskandiriyah, Contingency Operating Site Kalsu forms a crucial transit hub for the tonnes of materiel and thousands of soldiers moving out of the country, mostly towards Kuwait, in the coming two months.

The massive logistical operation has to be finished by December 31, in line with a security pact between Baghdad and Washington that US President Barack Obama said was on track this month.

"It's pretty big," said Captain Mark Alfers, the commander of the 606th Movement Control Team, a logistics unit on COS Kalsu.

"We've been here for eight-plus years, so there's just eight-plus years worth of equipment trying to get out of a single point."

Thanks to its strategic location, along the main thoroughfare heading south through Iraq, COS Kalsu will likely be one of the final five American bases left in the country, said Lieutenant Colonel Jason Hayes, commander of the 2nd Battalion of the 5th Cavalry Regiment.

It will be handed over to the Iraqi army along with a portion of materiel, but the exact date of its handover remains a secret for security reasons.

COS Kalsu serves as a "go-between for the smaller bases and the bigger hubs such as Kuwait or (Joint Base) Balad," a sprawling US base north of Baghdad, Alfers said.

As a result, between two and 20 convoys of up to 50 trucks apiece stop in Kalsu on their way south to refuel, and for passengers and drivers to get some rest.

Major General Jeffrey Buchanan, spokesman for US forces in Iraq, said that in the early part of October, 399 convoys with 13,909 trucks were used for the pullout in a single week.

At COS Kalsu, along with the countless flat-bed trucks and other vehicles, dozens of MRAPs -- "Mine Resistant Ambush Protected" troop carriers -- sit between rows of concrete blast walls that line the base's outer perimeter and parts of its interior.

Nearby, containers are piled up on top of each other, waiting to be carried out of the country, lugged out by contractor-driven trucks that regularly come and go.

Much of the military equipment remains hidden for security reasons.

"The biggest challenge is that this drawdown only happens once a war, once a conflict, so you can plan and plan for it but the plans keep changing," said Alfers. "You have to keep the enemy on their toes, so you can't really publish a plan."

These operations have been ongoing for several months, but Obama's October 21 announcement that all US troops would leave Iraq by year-end quashed any remaining speculation over potential for an American military training mission beyond 2011.

"The withdrawal operation really started to become big about a month ago," said Major Frank Cruz, a logistics officer on COS Kalsu. "Now, it's only getting busier."

Like his soldiers, Hayes does not yet know when he will finally leave Iraq. As to where they will go, some are hoping for a country less austere, like Germany, while others are looking to spend Christmas with their families.

Around 39,000 American soldiers remain in Iraq, stationed on 15 bases, including approximately 3,000 on COS Kalsu. That compares to peak figures of nearly 170,000 soldiers and 505 bases in 2007 and 2008.

Many of those still here have sent most of their belongings home and are living on the bare minimum.

And they are not the only ones who do not know when they will be leaving.

"The Iraqis would like to know as well -- it's frustrating," said Captain Ryan Edwards, commander of Bravo Company, 2nd Battalion, 5th Cavalry Regiment.

Edwards added that he was confident his domestic counterparts, whom he had been training for much of his deployment, were "ready".

Hayes painted a more nuanced picture of the forces Iraq would be left with.

"There's some security concerns," he noted. "I think the Iraqi army and police are capable of handling the current threat situation."

"I think if we saw a serious increase in violence, especially if that increase was caused by external influences, I think it could possibly exceed their capacity."

He added: "If it exceeds their capacity then my hope is that they'll be able to raise their hand and ask the world community for help. ... Whether they will or not that's the big question."