The attack on Yusufiyah began at just after eight in the morning. Round after round of rockets, then mortar shells and machine-gun fire racked the US Marines' base, in an intense and unrelenting barrage.
A relief patrol ran into a well-prepared ambush. Artillery and air strikes had to be called in, but even after that the battle went on for four more hours. The assault was part of a hidden, and largely unreported, war of attrition taking place in the most dangerous part of Iraq. With Fallujah now, in effect, in American hands, the fighting has moved on to north Babil and the so-called Triangle of Death.
About 120 militants are believed to have taken part in the Yusufiyah operation, and the Americans claim to have killed 40 of them. One marine was killed and seven others injured.
Such attacks have become increasingly common, and the scale of action, as well as the body count, is now among the highest in the country. The shadow of Abu Musab al-Zarqawi hangs over this bitter conflict. The US military and Iraqi sources say the Jordanian militant leader has taken refuge in the area after leaving Fallujah.
The 24th Marine Expeditionary Unit (MEU) is the American force involved in the operation, with the British Black Watch providing a more defensive, blocking role. Two or three times a week raids are carried out in isolated farms in the hunt for Zarqawi and his senior lieutenants, while firefights take place every day.
The two sides are acutely aware of the strategic significance of the towns of Mahmudiyah, Latifiyah and Yusufiyah and their hinterland. This is the home of the Sunni insurgency and also the routes through which its forces move to carry the war to Ramadi, Mosul, and Baghdad. The area was once, in effect, under insurgent control and was well known for kidnappings as well as frequent attacks on US and government forces.
Six weeks ago American forces launched Operation Phantom Fury to clear the area, but attention subsequently moved to Fallujah, and the insurgency is now back with a vengeance.
Some of the largest armament factories in the country were located here during Saddam Hussein's time. In two raids yesterday, at Haswah and Musayyib, US Marines and Iraqi National Guard found 100 artillery rounds, surface to air mortars, rockets, grenades, and boxes of Kalashnikov rifles.
There is no shortage of supplies for the resistance and the attacks have not only continued but increased. Lieutenant Colonel Mark Smith, the commander of the 2nd Battalion based at Mahmudiyah, said: "We have insurgents returning home from Fallujah and finding us on the way. With Fallujah over, the action has moved here. This is now the most dangerous place in Iraq. Increasingly, we are coming up against Zarqawi's people; they are better armed and better trained."
Lt-Col Smith had just returned from an all-night operation, and still had camouflage paint on his face. The raid, on a farm, followed information that Zarqawi was hiding there. They did not find him, but, Lt-Col Smith said, they caught two senior militant leaders.
"We have had lots of engagements and we have killed a lot. We keep on getting reports that Zarqawi is in this area. If he is we shall find him and we shall capture or kill him."
Lieutenant Michael Loring Mayne, who was involved in the battle at Yusufiyah, said: "What is very noticeable is that we are coming across well-trained fighters. In Yusufiyah they carried out a fighting withdrawal. That is not easy; it needs skill and discipline. We faced some pretty fierce and sustained fire and some of it was at pretty close quarters, some of my guys were pretty badly hurt.
"Pretty vicious things are going on here. We have had beheadings of people they suspect of helping us or the Iraqi government, and there are also murders of families of policemen and soldiers. This is about as nasty as it gets."
Colonel Ron Johnson, commander of the 24th MEU said: "This is the heart of the insurgency. If we can stop them here, it'll have a huge effect throughout the rest of Iraq. These are high stakes. If, after Fallujah, the insurgents can hold on to this area, they can rebuild, that is why they are fighting so desperately, and that is why we must destroy them."
An Iraqi National Guard officer said: "I have moved my family to live with relations in a village further away, and there they do not know what my job is. We had a grenade thrown at our former home, and my friend was among the 12 men who were kidnapped and then killed by the militants.
"I do not want to go alive into their hands. If I think that I am going to be captured, I would prefer to use my gun and kill myself."
A source with links to the insurgents said in Baghdad: "The Americans tried to control that area once before and failed. Why do they think they will succeed this time?
"The people are against them. They are afraid of Abu Musab [Zarqawi], but he is just one man; in the resistance there are many, and they are prepared to fight and die until the invaders are expelled."