Private First Class Martin Nieves has been homeless, on and off, ever since he left the US Army in January 2011. He has drifted from Washington, to Texas, to Pennsylvania, to New York, staying with family and friends for as long as they will have him and sleeping in shelters when he runs out of options. I met him on his first day at the Borden Avenue Veterans Residence, in Queens. "It's kinda small, but I can handle it," he told me, as trucks rumbled past along the waterfront.

At the last count, on a single night in January 2011, there were 67,495 homeless veterans in the United States. This was 12 percent fewer than the previous year, suggesting that aggressive efforts to tackle the problem are starting to make a difference. The Secretary of Veterans Affairs, Eric Shinseki, has won increased funding for homelessness programs every year, in an era of steep budget cuts. Veterans advocates praise his efforts - but says much more needs to be done.

In Iraq, Nieves was a bodyguard for a senior officer at Camp Taji, north of Baghdad. "Everywhere he went, I went," Nieves said. "We were shot at. Three times we got grenades tossed at us. Nobody died, thank God. But I can't keep a job now because of my neck, my back, my ankles, my wrists. It was the time we got bombed, banging up against the Stryker. My best friend who was right by my side lost his eye from the shrapnel."

An initial psychological screening came up positive for Post Traumatic Stress Disorder and depression, but when he went to schedule a primary care appointment in July, he was told to come back in December. Because he didn't get a full honourable discharge - "I started being late purposely so that I could get kicked out" - he only receives partial benefits.

"I just stay awake," he said. "In Iraq while we were sleeping there was artillery coming in almost every night. Now I don't go to sleep. I used to be fun, going out all the time, spending time with my nieces and nephews. Now I just stay to myself as much as possible. I've been having a lot of anger issues and I don't want to take it out on anybody."

Nieves has eight sisters and one brother, but he has burned through one relationship after another. To Shad Meshad, who set up the National Veterans Foundation when he returned from the Vietnam war, this is a familiar story - a young man altered by his wartime experiences, alienating the people he needs most.

"Something happens and you retreat, you walk out of the house. You can't relate to your most intimate people, you don't have a job and you don't have money. So you get in your car, if you have a car, or you get on a bus, and you just ride, trying to think, just like a kid running away that had an upset with his parents, who realizes there's no place for me to go. Well, the difference between a child and a combat vet is he can survive anywhere. If he's been in Iraq or Afghanistan this is a piece of cake here - I can find shelter. And you think you're just gonna do it for the night," Meshad said.

The scale of the challenge facing the Veterans Affairs (V.A.) administration is immense. Veterans filed more than 1.3 million benefit claims in 2011. "This system is going to be overwhelmed," Defence Secretary Leon Panetta recently told a congressional hearing. "Let's not kid anybody - it's already overwhelmed."

It took Ryan Charles a year to even ask the V.A. for help, after his stint in the Army turned sour, when he asked for a discharge after one tour to Iraq and another to Afghanistan. "From my leaders I was hearing 'you ain't gonna be s***, when you get out of the Army what are you gonna do? We're in a recession.'"

He has been looking for work ever since. At security firms, he is told that he needs proper certification. Hotels and shops don't call him back, although he is presentable and well-spoken. On his Curriculum Vitae, the entries jump from high school, to Iraq, to Afghanistan, to unemployed. "I feel like I'm carrying around a blank piece of paper," he said. Last year, the unemployment rate among his peers, veterans aged between 18-24, was 29.1 percent.

Charles keeps clothes at his mother's apartment in Brooklyn and sometimes takes showers there, but he sleeps in his car, across the street. His mum can't afford to take him in, but in any case, six years in the Army have changed him. "Everything's different since I've been back. I was gone for a long time and my philosophy was 'no news is good news,' so I only called her twice a year," he said.

The way he sees it, things could be worse. "I guess it's just the infantry lifestyle rubbing off on me still," he said. "I've slept in abandoned buildings in the field, so sleeping in a car is money to me."

At his first psychological screening, the doctor told him he may have PTSD, may have depression and may be drinking too much. Charles has been suffering from dizziness and memory loss ever since an Afghan soldier walking a few meters ahead of him stepped on a mine and lost both his legs in the explosion. He is slowly finding out what the V.A. can do for him, but on average, it takes eight months to process a claim.

Secretary Shinseki has set a goal of ending veteran homelessness by 2015, but this target is viewed with skepticism by charities. Veterans are twice as likely as civilians to become chronically homeless and almost 150,000 former servicemen and women spent at least one night in a shelter or emergency housing last year.

"This is a situation that nobody really wants to know goes on, because it's embarrassing," said Meshad. "We need to be appalled that we allow this in this free country and I don't know what appals people any more."