It wasn't his first tour in Iraq, but his second and third when Joe Callan began wondering how long his luck would last — how many more months he could swerve around bombs buried in the dirt and duck mortars raining from the skies.

It was only natural, considering the horrors he'd seen: One buddy killed when a mortar engulfed his tent in flames. A fresh-faced Marine sniper dead (also a mortar) on his first day in Iraq. A 9-year-old Iraqi boy, blood trickling from his head, after he was mistakenly shot by U.S. troops.

Three tours in four years and Callan wanted out. Out of Iraq, out of the Marines.

"I became numb," he says. "I just wanted to be home. And that became more intense each time."

When Callan did return to New Mexico, he couldn't sleep. He drank heavily. He had a short fuse. "I knew," he now says, "I was different. But I didn't think it was going to be that bad."

Maj. Jeff Hall's world imploded after his second tour in Iraq.

Overwhelmed with guilt and rage, the 18-year Army veteran became so depressed that one day he lay on the ground and pointed a pistol at his head. The only reason he didn't kill himself, he says, is he didn't want his two daughters to discover him. "I couldn't do that to my kids," he says. "I had seen people with their heads blown off."

But the war had pushed Hall to the brink. "I had no peace at all," he says.

No peace — on the battlefields of Iraq and Afghanistan, or in the minds of men and women who fought there. Callan and Hall are among hundreds of thousands of U.S. troops who've served multiple tours; they're also among the tens of thousands diagnosed with post-traumatic stress disorder.

That is not a coincidence.

With two long wars — Afghani- stan is in its ninth year and Iraq just entered its eighth — the U.S. military finds itself straining to maintain a steady flow of troops. More than 2 million men and women have been deployed to serve in both conflicts, and more than 40 percent of them have served at least two tours, according to military records.

Nearly 300,000 troops have served three, four or more times.

For these men and women, life becomes a revolving door of war, home, then back to combat — sometimes within months — as they face the same dangers, the same stresses and the same agonizing separation from family.

Multiple tours, according to studies, have been linked to stress, anxiety and PTSD, which can be marked by nightmares, flashbacks, angry outbursts and insomnia.

After two Iraq stints 10 months apart, Hall wanted to be left alone.

He didn't think he had helped the Iraqis or accomplished anything.

Looking back, Hall remembers the day he realized something was terribly wrong. It was after his first tour, when his family was having dinner at a restaurant and his daughter, Tami, then about 12, refused to touch her steak because sour cream had gotten on it.

Hall began crying. His family was stunned. So was he.

What Hall didn't reveal was his daughter's fussiness had revived memories of a very poor family in Iraq that would regularly pick up gas for cooking at a propane station he had guarded. Their two girls — close to his daughters' ages — were so emaciated their skin hung like loose cloth.

"I could just see the faces of the little girls," Hall says. "It triggered a feeling of sadness and anger."

But suicidal thoughts didn't surface until after Hall's second deployment, which was more aimless than the first. "It was like we were driving around until we got blown up," he says.

In the first few months, Hall's brigade lost more guys than the entire year in his first tour. One day a Humvee under his command ran over a massive bomb, killing two soldiers, seriously wounding another.

"I felt shame, absolute shame," Hall says. "I was suffering from guilt. We were having no results. I described it to the psychologist two years later ... It was like a complete loss of identity ... and how you think life is or should be."

His wife, Sheri, who had been encouraging her husband to get help, finally called his commander. That led to a civilian psychologist and a diagnosis of PTSD.

"I thought my career was over," Hall says. "I thought, 'What am I going to do?' At the same time, I had this feeling of, 'Aha, there IS something wrong. I'm not making this up.' "

A 2009 report of Army troops in Afghanistan found the rate of psychological problems rose significantly with the number of deployments: 31 percent for three tours, more than double the rate of those with just one.

In Iraq, the survey found nearly 15 percent of Army troops who served two tours suffered from depression, anxiety or traumatic stress, more than double that of single-tour soldiers. When it came to PTSD alone, the rate was almost 2 1/4 times higher for two deployments compared with one.

"We just don't know whether it's combat exposure, repeated separation from the family or (not enough) time off," says Lt. Col. Paul Bliese, director of the division of psychiatry and neuroscience at the Walter Reed Army Institute of Research. "All of those are reasonable explanations."

Hall found help in an intensive three-week treatment program at Walter Reed he attended with his wife.

"It gave me hope that there was a chance I could heal," he says.

Hall is now creating the resilience campus at Fort Riley, Kan. The program will help soldiers and their families rebound from multiple tours and deal with the stresses of war and everyday life.

Still, he does not consider himself cured of PTSD.

"I don't believe that you get over it," he says. "I think you learn not to let it control you. You learn to control it."

Joe Callan ended his 11-year stint in the Marines two years ago, and it was then his life unraveled in a familiar pattern: Depression. Insomnia. Anger.

Callan credits his wife, Katy, their three kids and other family with helping him recover. Callan has been in and out of counseling; he has little time for that kind of stuff.

"I have to suck it up," he says, "because people are depending on me."

He has found renewed purpose in a job: He's now an organizer for Iraq Veterans Against the War. Soon, he hopes, this war will be over.

"I just want to have a small farm," he says, "hang out with my family, grow vegetables and be left alone. I just don't want to be a part of it anymore."