Washington ? Soon after he took over as the new U.S. military commander in Iraq Tuesday, Gen. Raymond T. Odierno greeted the U.S. troops standing before him in Arabic: “As-Salam Alaikum,” or peace be upon you.

For a soldier once known for his aggressive tactics and his impatience with local residents, his budding Arabic marked an extraordinary evolution.

When he arrived in northern Iraq in 2003 as the 4th Infantry Division commander, the physically imposing Odierno was more likely to level a community than reach out to it.

On his second tour this past year, he and his fellow soldiers mastered Iraq’s tribal structure, customs and the finer points of counterinsurgency, which helped lead to a dramatic drop in violence.

Odierno, who succeeds Gen. David Petraeus, is charged with the task of maintaining the security gains of his predecessor while managing a U.S. troop drawdown.

To many in the military, Odierno personifies the transformation of the American military in Iraq.

“Gen. Odierno didn’t know much about counterinsurgency five years ago. He reflects the American Army, which also didn’t understand counterinsurgency very well,” said retired Lt. Col. John Nagl, who drafted the counterinsurgency manual with Petraeus. “You can’t kill or capture your way out. I think there was a time when the Army believed that” it could.

Odierno’s career in Iraq began in frustration. The 4th Infantry Division didn’t take part in the invasion. Stuck in Turkey and blocked from crossing the border, it moved in after the invasion and deployed in Saddam Hussein’s northern hometown of Tikrit days after Saddam’s statues were toppled around the country.

American forces treated Iraqi citizens as potential combatants. They traveled without translators. Each innocent civilian killed was seen as an isolated incident, not an igniter of future violence.

Odierno’s troops were known as especially aggressive and unsympathetic, asserting that the mostly Sunni community around Tikrit was filled with Saddam backers. They kicked down doors, destroyed homes, killed civilians and arrested thousands, sometimes seemingly indiscriminately.

Odierno seemed to ignore the early signs of the insurgency, and some charged that his tactics emboldened it. When his unit found Saddam hiding in a spider hole in December 2003, Odierno declared that the insurgency was over. But its best days were just around the corner.

Petraeus encouraged soldiers to move into small outposts and reconcile with former fighters, and soon Odierno and his fellow troops embraced the strategy, even though it called for troops to put themselves at risk.

“We were all talking about the right things but nobody drove it” until Petraeus came up with his plan, said Gen. William Caldwell IV, who served with Odierno at the beginning of his second tour and is now commander at Fort Leavenworth, Kan.

Odierno began learning the religious and tribal breakdown of every district. He learned Arabic and walked around neighborhoods as did the captains in charge of those districts. Odierno was constantly studying maps and fine-tuning the details of the plan. He assigned each outpost and monitored violence in the capital and some of Iraq’s biggest hot spots.

It worked. Violence is now at one of its lowest levels of the war. So far, this month, only two U.S. troops have been killed in hostile action.