In April, 2,000 Marines fought for three weeks and failed to take Fallujah (search) from its insurgent defenders. This time, war planners sent six times the troops, who fought their way across the rebel city in just six days — far more quickly than expected, the Marine general who designed the ground attack said Sunday.

"We had the green light this time and we went all the way," Maj. Gen. Richard Natonski (search) told The Associated Press.

Natonski said he and other planners took lessons from the failed three-week U.S. assault on the city in April, which was called off by the Bush administration after a worldwide outcry over civilian deaths.

This time the military used swarms of aircraft — more than 20 types — that pounded the city before and during the assault. Troops also faked attacks before the assault to confuse enemy fighters.

"Maybe we learned from April," Natonski said. "We learned we can't do it piecemeal. When we go in, we go all the way through."

Privately, U.S. military officials say April's assault was botched by the Bush administration which forced the Marines to attack with insufficient forces on just a week's notice and then called off the assault before the city was taken.

For the latest assault, commanders had time to plan. Also, the Iraqi and U.S. governments were determined to wipe out the insurgent nest. And the Iraqi troops, who melted away in April, stood their ground.

Even the worldwide outcry was muted this time, by revulsion at an insurgency blamed for grisly beheadings of hostages.

Natonski described the first six days of ground war as a "flawless execution of the plan we drew up. We are actually ahead of schedule."

As quick as the assault was, perhaps thousands were killed and maimed, most of them Iraqi defenders. Natonski put the toll of guerrillas killed at more than 1,200.

A military statement Sunday said that 38 U.S. troops had been killed and 275 were wounded so far in the operation.

There is still no estimate of civilians killed or wounded in the assault.

On Sunday, Marines and Army troops still battled pockets of hardcore defenders scattered inside the Sunni Muslim (search) stronghold. Behind U.S. forces, Iraqi troops were engaged in the painstaking task of clearing weapons and fighters from every room of each of Fallujah's 50,000 buildings.

Bands of rebels were still roving neighborhoods crushed by tons of U.S. bombs and shells. The holdouts are harried by U.S. forces who occupy — but have yet to subdue — the entire city.

"There are groups numbering from five to 30," Natonski said. "They're trying to get behind us."

Military officials said it would take days to finish the fight.

As troops uproot the insurgents, contractors are supposed to swarm into Fallujah in coming weeks to cart away rubble, repair buildings, and fix the city's water, sewer and electricity systems.

The Iraqi government has already picked leaders for Fallujah, and thousands of Iraqi police and paramilitary forces have been recruited to try to impose order — critical to the U.S. goal of setting conditions for elections in Fallujah and the rest of Anbar province.

To prevent the insurgents' return, Iraqi forces will halt all traffic flowing in and out of the city — once roads reopen — checking IDs and looking for suspects, Natonski said.

U.S. and Iraqi leaders have long vowed to deal with Fallujah, which in May became a virtual independent rebel city-state and nationwide model for rebellion. One event in August crystallized their resolve.

Back then, an Iraqi National Guard commander acting as a liaison between Fallujah and the U.S. military, Lt. Col. Sulaiman Hamad Ftikan, was beaten to death by mujahedeen inside the city.

"That's when we realized Fallujah was the bright ember in the ash pit of the insurgency, and we needed to douse it," said Lt. Col. Dan Wilson, a planner with the 1st Marine Expeditionary Force.

Battle planning began in September, with Natonski given responsibility for the combat phase, Wilson said.

Hundreds of other U.S. military and civilian planners designed the overall effort, which is intended to mimic the ongoing post-siege rebuilding under way in Najaf, Wilson said.

Several pre-assault tactics made the battle easier than expected, Natonski said.

Insurgent defenses were weakened by bombing raids on command posts and safe houses. And in the days before the raid, ground troops feinted invasions, charging right up to the edge of Fallujah in tanks and armored vehicles.

Natonski said these fake attacks forced the insurgents to build up forces in the south and east, perhaps diverting defenders from the north, where six battalions of Army and Marine troops finally punched into the city Monday.

The deceptive maneuvers also drew fire from defenders' bunkers, which were exposed and relentlessly bombed before the ground assault.

"We desensitized the enemy to the formations they saw on the night we attacked," Natonski said.

Another key tactic was choking off the city, the responsibility of the 2nd Brigade of the Army's 1st Cavalry Division, Natonski said.

That move prevented insurgents from slipping out of the city during the assault, although many, including top leaders like Jordanian Abu Musab al-Zarqawi, Sheik Abdullah al-Janabi and Omar al-Hadid, are thought to have fled.

"We never expected them to be there," Natonski said. "We're not after Zarqawi. We're after insurgents in general."