In his first combat deployment, he was shocked at the violence that unfolded around him. He remembers his tours as "scary and exciting; mostly scary." He was in a convoy that hit a buried bomb.

"The vehicle commander was tore up pretty bad; I got a concussion," he said in slow, precise tones.

After his two tours in Iraq, he transferred to another unit and is now aboard the amphibious assault ship Makin Island, preparing for deployment with the 15th Marine Expeditionary Unit to an unspecified location.

Over time, revenge has faded in his mind. He's a squad leader now, a mentor to young Marines, and his tone is more even-tempered: There is a mission out there that must be accomplished.

"War is one of those things that have to be done for the greater good, but it's one of the most horrible experiences you can go through," he said. "I'm glad I did it for our country, for our Corps, and for myself. We were serving a purpose over there, not just for the United States but for the Iraqi civilians."

He knows that by enlisting he missed out on a more carefree life, but he has no regrets. When he goes home, he notices that his buddies seem to take things for granted and don't realize the dangers of the world.

"I love my friends dearly, but after a while I can't wait to get back with Marines," he said.

But the day will come when Wallek leaves the Corps. And that future is bright: He's married to a graduate student at Texas A&M University. They have a 4-year-old son.

Still, he said, "if I get out, I know I'll miss the brotherhood we have in the Marine Corps."

The burden of service has weighed most heavily on families.

Marine Staff Sgt. Michael Weber, 28, has deployed three times: twice to Iraq, once to Afghanistan. He said he probably would have made even more deployments except for a three-year stateside assignment working as a rifle range instructor.

"I was trying to make my first marriage work," he said with a mix of humor and sadness.

At the height of the Iraq war, Marines referred to their lives as seven-and-seven: seven months in Iraq, then seven at home, then seven back in Iraq.

The result was a kind of dual existence in which Weber said his mind was constantly torn between family and duty.

"The invasion [in 2003] was the worst for the family, one letter home in a month," Weber said. "It's better now with satellite phones and email, but it's still tough on families."

He's remarried and hoping again to deploy. Years of packing 100-plus pounds of gear over miles of rutted roads have left him with back problems. Until the doctor gives the OK, he's got desk duty at Camp Pendleton.

"As much as nobody likes wars, I'd go back in a heartbeat to be with my brothers," Weber said. "For the infantry, wartime is the only time you get to do your job for real — a chance to see how you react."

Donnelly, who had enlisted in the Marines out of high school before Sept. 11, said there is a consuming quality to war. It is what you spend all your time training for and provides a focus that few civilians understand. It is a kind of addiction that is hard to shake, even after leaving the service.

He was on guard duty at the United States embassy in Costa Rica on 9/11 and hoped he would be assigned to the assault on the Taliban government in Afghanistan in late 2001. That didn't happen, but he was overjoyed to be part of the push into Iraq.

After the fall of Baghdad, Donnelly decided that eight years in the Marine Corps was enough. He had fought his war and — he thought — helped the U.S. win a quick knockdown. A sergeant, he opted not to reenlist.