The American army is renowned as the most advanced fighting force in the world. Keeping its fighting personnel supplied demands an equally advanced logistics system.
The US supply system is large and versatile.
Supplies for ground forces are organised by the Combat Service Support (CSS) arm of the military.
There are more than 10,000 five-tonne cargo trucks in its inventory alone.
These, together with large numbers of other, specialised vehicles, carry everything from water, food, fuel, and ammunition to specialised tools, clothing, medical supplies and replacement parts for fighting vehicles, to the front line.
Support units catering for every military requirement are attached to each American fighting division. A list of units in the region records the presence of the 1st Dental Battalion, illustrating the scope and range of US support services.
Huge numbers of trucks are on the move
Sustaining the US forces engaged in fighting across large distances in southern Iraq demands vast logistical reach and planning.
Correspondents have reported vast columns of supply vehicles snaking for miles across desert roads.
A typical supply column for the US Marines, observed moving up to the front line this week, was estimated by a New York Times reporter to be carrying about 160,000 gallons of fuel and 180 tonnes of ammunition.
Provision of water is also vital for troops engaged in desert warfare, while heavy armoured vehicles such as the M-1 Abrams tanks consume large amounts of diesel fuel.
Concerns about overstretched supply lines and a series of attacks by irregular Iraqi forces appear to be prompting a rethink in American tactics.
"The long distances we have travelled make it hard to push that amount of logistics - water, fuel, ammo and food over the vast
area that's been covered," Marine First Lieutenant Tom Elssinger told the Reuters news agency from southern Iraq.
On Sunday, the dangers faced by convoy crews were demonstrated when Iraqi state television showed five captured US personnel - all from a supply column - who had lost their bearings and run into an ambush.
And in southern Iraq, US Marines have fought a series of battles near the town of Nasiriya against Iraqi forces attempting to stop US supplies destined for troops further north crossing two key bridges over the River Euphrates.
Despite having to battle to keep supply routes open, the US says it is confident that it can protect its logistical forces.
One logistics commander told the New York Times: "We're not just truck drivers. We're truck drivers with guns.''
But as the distance between safe territory and the front line grows, military analysts say keeping the supplies moving will be vital if the military campaign is to stay on course.