US soldiers fighting militants in Iraq's Sunni heartland are facing a dramatic daily struggle for survival, reports the BBC's Paul Wood, embedded with the 101st Airborne Division.
"Stop, back up, check that's nothing that's going to pop us," says the officer in charge of the armoured Buffalo inching its way up the desert road.
We're travelling through the Sunni heartland, south of Tikrit, with a bomb disposal squad of the 101st Airborne Division.
It's slow going. Every patch of disturbed earth, plastic bag, or wire is suspect. It will take six hours to cover the 20 miles (32km) to the base we're heading for. This road is known as a hotspot for IEDs (improvised explosive devices).
Although most violence in Iraq is sectarian - Iraqi killing Iraqi - most of the violence directed against US forces comes from Sunni insurgents. The roadside bomb - or IED - remains their preferred method of killing Americans.
Suddenly, there's a thud and smoke on the road ahead. The first vehicle in the convoy has been hit. "Stop, stop, stop," comes the command over the radio. "Anybody hurt?"
Only the thick bullet-proof glass has been damaged, it turns out. Everyone inside is fine.
'Safer' with the Americans
For years American soldiers complained that their vehicles made them vulnerable to roadside bombs. After a huge Pentagon programme to provide better protection, you rarely hear that complaint in Iraq these days.
The soldiers spot a command wire, leading back several hundred metres to a trench. Far away, a figure is seen running in the distance. They give chase.
By the time we catch up, a number of Iraqi men have been arrested in the village. Hands tied behind their backs with flexicuffs, they squat miserably on the ground, facing the outside wall of a house.
Many have tested positive for explosives but, since nitrate fertilizer can also give the same result, the soldiers can't jump to conclusions.
The risk for the Americans is that humiliating these men could turn the whole village against the coalition. But, as he is questioned, the head man says he feels safer with the Americans around. It's the insurgents he fears.
Eventually, it emerges that one of the detainees isn't from the village, a complete stranger in fact. None of the village men have ever seen him before. Since he's wearing black, like the figure seen running, the squad think they've got their man.
On the way out, the head of the village tells me he is not angry at the Americans. He much prefers them to the Iraqi forces. When the Iraqi police and army come, he says, they break things and steal. The Americans don't do that.
Orders to shoot
On the way back, the squad gets a bad scare. A car comes over the brow of a hill and fails to stop. A warning shot is fired. Then the troops fire into the engine, fearing a car bomb.
Two Iraqi men get out of the vehicle, hands raised, the red dots of the Americans laser sights dancing on their chests. They both realise they have come very close to being killed.
"I'm very, very sorry," the Iraqi man says, over and over. He explains that his sister has been taken to hospital and he's rushing to see her.
The lieutenant explains that many troops have been killed by car bombs - and his men have orders to shoot at vehicles which do not stop. But the dilemma for the coalition is that what you have to do to protect yourself can undermine the support you need to win in the end.
American commanders insist that their counter-insurgency strategy in Iraq is starting to work. There have been many "turning-points" in Iraq, much "light at the end of the tunnel" so this message is being treated with some scepticism.
And to the ordinary soldier, Iraq seems as dangerous as ever. But the Pentagon's statistics show that the number of attacks on US forces is down. That is the case, say senior commanders, because ordinary Sunnis have decided to turn against the insurgency.
Central to US strategy are what are called, without irony, the "concerned local citizens". Often masked, and wearing yellow T-shirts to identify them, you see them manning checkpoints with their Kalashnikovs.
They are recruited through Sunni tribal leaders, who are paid, some would say bribed, by the Americans to keep the peace. But they work with the police - and sometimes they have been known to work with the insurgents.
We join a patrol to the nearest small town. Within sight of the police checkpoint, the patrol stops to meet the locals. They chat to an elderly Sunni who has fled Baghdad. Suddenly the relaxed discussion is interrupted by sniper fire.
To the right of the armoured jeep, a soldier's been hit. He crumples. For some of these young soldiers - just 18 or 19 years old - it's their first time under fire. "What should I be doing sergeant?" one shouts out, panicked.
Their sergeants, now on a third tour of Iraq, react instinctively, sweeping their automatic weapons up and down the road, looking for the sniper.
The medic breaks cover to get to the injured man. Mute with shock, he's losing a lot of blood. The bullet passed through his leg. But it missed the artery.
The soldiers want to hit back. But where? No one can see the sniper, who is probably long gone by now. For the troops, it's immensely frustrating, but anyway, the priority now is to evacuate the casualty.
The Americans must win here, in the Sunni heartland, if they are to leave Iraq.
Even if things are turning around, their local allies remain uncertain, the population divided, the casualties, although reduced, keep coming.
There is much still to do.