"In a mosque?" Johnson asked one of the Iraqi soldiers who found the weapon.

"In a mosque," the Iraqi confirmed.

"Not good."

"No. Not good."

The Iraqi troops also discovered a cache of clothing and a student's copy book filled not with school lessons, the Iraqis said, but with Arabic instructions on firing weapons. The figures "RPG 7" appeared in bold English letters at the top of one page.

It wasn't the first such find, and it only added to Johnson's convictions on how to handle his little piece of Fallujah.

By the fifth day in the city for Alpha Company, 1st Battalion, 3rd Marines, the insurgents who have held Fallujah for months had become more reluctant to show themselves. But in the several-block area assigned to his company, Johnson's Kane'ohe-based Marines were treating every door, every window, and every building as a potential death trap.

"Virtually every building we've entered had something," Johnson said. Of several mosques the company had searched, only one was empty of weapons — and the hospital serving as the company command post had held ammunition, he said.

"They know our (rules of engagement)," Johnson said. "They know we're going to be careful with sensitive sites, and they take advantage."

Meanwhile, a neighborhood packed with explosives was devoid of civilians. No one in the company had reported finding a single family. No women, no children.

"The only thing here," said Lance Cpl. Cody Weathers, "are dogs and people shooting AK-47s at us."

And so, in Johnson's mind, being careful with his Marines' lives took the paramount position. Weapons stacked in a home? Bring in engineers or explosive ordnance disposal troops or, if necessary, light it up with an AT-4 antitank rocket. Two buildings suspected of harboring insurgents and weapons were destroyed using Javelin missiles.

"We're not here to tear down the city," he said. "But I'm here to get my boys home. I'm responsible for husbands, sons, fathers, uncles of American families."

Alpha Company's job five days into the invasion of this city was simple: make sure insurgents didn't retake areas of Fallujah that the 1st Battalion, 3rd Marines and other Marine and Army units had sped through on their way to objectives in the city's southern districts.

Already, Alpha company's officers worried that rebels had "infested" several blocks. So the company had begun a careful, painstaking, block-by-block sweep through its assigned area. That meant at least 20 controlled detonations over the course of the day. As firefights rang out in other sectors of the city, Alpha was dropping mortar shells on suspicious buildings, moving Marines through buildings and destroying arsenal after arsenal.

Much of the job fell to Lance Cpl. Christopher Gamboa, an 18-year-old from San Antonio. When an Alpha Company platoon entered a house and discovered a 55-gallon drum with a telephone, with wire attached, sitting on top, Gamboa got everyone out and called in an Army explosive ordnance disposal attachment. For one of the few times that day, the suspected booby trap was a false alarm.

"But we're not taking any chances," Gamboa said.

A sniper team watched over Alpha's three platoons as they fanned out across the city. The two men, during breaks between watches, showed off pictures of their young children.

Cpl. Travis Facenda had yet to see his daughter, born two months before. Cpl. Brad Thomas, a 30-year-old Texan who joined the Marine Corps three weeks after the Sept. 11 attacks, had photos of his wife and 3-year-old son in the liner of his helmet.

"Just waiting to get back to them," Thomas said.

As they shared photos, three Iraqi soldiers moved up to take observation positions on the hospital roof. That raised some Marines' eyebrows. The Iraqis had developed a reputation for being trigger-happy, and Alpha Company's Marines placed them on the side of the building farthest from areas where friendly troops were working the streets.

Johnson said the Iraqi platoon of 41 soldiers arrived four days before the Fallujah operation began, leaving little time to integrate them into the company.

By the time the company crossed into the city, that number had fallen to 26. Some, Johnson was told, were sick or sent home, but there seemed little doubt that many had deserted.

Also, the remaining soldiers required occasional lessons in Marine discipline. The company had given them a sledge hammer and other tools to use in breaking into and clearing buildings. They lost the tools almost immediately, leaving them at a previous company position — prompting a chewing out, with Arabic translation, from the company's executive officer.

But overall, Johnson said, he'd been surprised at how well the Iraqis had performed.

"I'll be honest, I was concerned at first," he said. And he still didn't feel comfortable placing them in frontline positions. But they had proved valuable at sniffing out traps and weapons caches — in the courtyard of a mosque thoroughly searched by Marines, the Iraqis discovered a collection of 155mm artillery rounds buried in the courtyard.

As the sun set, Alpha Company had completed one of its most difficult tasks — turning over custody of roughly a dozen Iraqi prisoners captured over the course of the day.

Nearly all said they were residents of the city, staying to protect property or their families, but the Marines scoffed at such explanations. When the prisoners were quizzed, Johnson said they often didn't know landmarks or streets of the neighborhoods they claimed as home.

Interpreters said they thought a prisoner captured earlier in the operation was Syrian, feeding suspicions that foreign fighters were playing a large role in the Fallujah battle.

The thoughts of most of the Marines, however, were far away from factors as abstract as whether the rebels targeting them were from around the corner or from around the globe.

"We've been watching this war and wanting to come do this for almost two years," said Cpl. Niles Holland, a mortar team leader from Boston. "We've just been dying to get here and prove that Hawai'i Marines can do the job.