Vietnam veteran Rod Bales says he still doesn't like to sit with his back to the door in an unfamiliar place. Not being able to see who's coming and going makes him feel anxious, he says.

Bales joined the Army with a high school friend in February 1966. The two were caught in a blizzard near Macedon, and took shelter in a barn. They dreamed of being in the hottest place they could think of. The steamy tropics of Vietnam seemed like a good alternative to Upstate New York in the middle of winter, Bales says.

Only 17 at the time, Bales says he thought enlisting was the right thing to do, and he figured he'd be drafted anyway.

"Enlisting in the service was like a higher calling, a noble thing to do," he says.

Bales came home about three years later in the early stages of alcoholism and post-traumatic stress disorder. He attempted suicide three times.

Bales has been sober for 14 years and says he no longer thinks of suicide. But he still suffers from PTSD, and says he understands why thousands of veterans call the Veterans Crisis Line, a toll-free hotline for veterans and active service members, at all hours of the day and night. The calls come into a call center run by the Canandaigua VA Medical Center, which is part of the Department of Veterans Affairs' vast network of health-care facilities.

The department created the Veterans Crisis Line in 2007. The number, 1-800-273-TALK (8255), is the National Suicide Prevention Line. Calls from veterans and active members of the service are then directed to the Veterans Crisis Line, which is staffed by specially trained mental-health professionals.

The toll-free hotline number is all but tattooed on veterans' palms. It's promoted on the VA's Web site and in VA hospitals and outreach offices across the country. Active-duty service members are also given information about the Veterans Crisis Line.

The calls form a complex emotional arc. A caller might be frustrated because he needs transportation to pick up a new pair of glasses. Another might be depressed because his spouse and children have left.

And then there's the caller who says something like, "I have a gun in my lap and I'm planning to use it."

The Veterans Crisis Line call center is sequestered on an upper floor of the Canandaigua VA Medical Center, about 20 minutes east of Rochester. Call responders, many wearing phone headsets, sit at desks with large computer screens that can provide responders with important information about the people on the line, such as their medical history, address, military status, and records of prior calls.

With its dimly lit cubicles and the low, but constant hum of voices, the call center is a nimble hive of caretaking. The call center has grown from 15 responders in 2007 to about 200 today. Approximately 20 to 24 responders staff three daily shifts, fielding calls 24 hours a day, seven days a week. The highly trained responders listen to the veterans and assess the urgency of the calls.

Callers range from active service members sitting on a hillside in Afghanistan, to a homeless veteran calling from a phone booth in San Diego. Most of the callers, about 75 percent, are men.

And the volume of calls is so high, it tests the imagination.

From October 2010 to September 2011, responders handled 148,198 calls. More than 90,000 were from men and women who identified themselves as veterans or active service members, and more than 10,000 identified themselves as family members or friends of veterans or active service members. And 6,177 of the calls involved rescues of people who were contemplating suicide or already engaged in the act.

Since opening in 2007, the call center has handled 478,439 calls and rescued more than 17,500 suicidal callers. The quantity of calls reflects a stark reality: a member of the military service commits suicide every 36 hours, according to the VA.

The goal for these callers is prevention and risk reduction, which frequently requires addressing multiple health problems, says Janet Kemp, the VA's national mental health director. Tackling the suicidal thoughts, for example, often involves helping the caller gain sobriety, she says.

The responders do not provide individual counseling: they are there mostly to intervene. They connect callers with mental-health professionals at a nearby VA center. If there isn't a VA center close by, or if the callers require support not offered at that facility, other arrangements are made, Kemp says.

If responders sense that callers are in imminent danger, either as a threat to themselves or to someone else, responders are trained to ask a sequence of questions.

"They first talk about whatever the veteran wants to talk about," Kemp says. "Usually, it's a very open-ended conversation: 'You sound like you're upset. What's bothering you?'"

Then, Kemp says, responders ask, "Have you made plans? Do you have a gun? Where is the gun right now? Do you have pills? Have you taken any of the pills?"

Handguns and drug overdoses are responders' biggest worries, Kemp says. Some estimates indicate guns are responsible for as many as 70 percent of suicides among veterans and active service members. Pills are also readily accessible, Kemp says, but they aren't always effective.

"One of the things we know is that if we ask them very specific questions, they are more likely to tell us the truth," she says. "So it behooves us to be specific with them. Maybe that's because they've done the hardest thing and made the call."

Responders will ask callers if they can "stay safe until the next day," when a mental-health professional can call on them, Kemp says.

"If they say 'no,' then we send help," she says.

After the crisis has passed, responders make sure the callers connect with the right professionals.

"We check within 24 hours to make sure that the [VA] suicide prevention coordinator did pick up the referral, and followed up with them," Kemp says. "If for some reason they can't find the person, we send someone out to do a welfare check."

Further calls are made after 72 hours and after two weeks to make sure the caller is engaged in care. And after a couple of months have passed, responders make "compassionate callbacks" to see how the caller is responding to care.

"We have to make sure that they not only haven't somehow fallen through the cracks of the system, but that they're also feeling better," Kemp says.

Repeat calls to the Veterans Crisis Line indicate that the veteran or active service member hasn't connected to the right type of help, or that the support they're receiving isn't working for them. The good thing, Kemp says, is that they're still trying to help themselves.

"We work with their [mental health] care providers on a treatment plan, so that when they call back, we're not telling them something different than their provider is telling them," Kemp says.

For example, the care provider will often help the veteran or active service member create a plan to cope with anxiety, depression, or suicidal thoughts.

"Maybe it will make the person feel better if they go bowling or to see a funny movie," Kemp says. "So planning for this ahead of time, the person calls a friend or a sibling to make an arrangement. They both know that going bowling or to the movies means, 'I'm feeling bad. Can you spend some time with me?'"

These details are available so the responder can ask, "Have you thought about calling your brother and going bowling?"

The call center's responders have varied backgrounds. Many are veterans themselves, Kemp says, or have worked with the VA and are familiar with the population served by the MedicalCenter. Some responders have degrees in psychology or social work.

The call center tends to attract people who are drawn to the emotional intensity of the work.

Mary Woodruff, a licensed mental health counselor, is a good example. She began working at the call center in 2005.

"A big piece of the job is the intensity of it from the moment you hit the ground," she says. "It's scary in the beginning."

Woodruff says many of the callers need someone to stop and listen to them. Listening without judgment is rare, she says.

"But it's absolutely crucial to be able to do this," she says. "I'm trying to be as present as possible when I'm on the phone because it can mean someone's life or death if I miss something."

Woodruff says she can usually hear a change in the caller's voice that lets her know that he or she is going to be OK.

"I've heard the call where someone says, 'I'm going to end this. Come and get my kids,'" she says. "But if you stick with them and let them be heard, somehow the process works as it's supposed to."

Shift supervisor Dan Brown says the hardest part for him was accepting that some people won't seek help.

A woman once called on behalf of her sister who had already completed her suicide about an hour earlier, Brown says. The caller didn't know what to do, so she called the Veterans Crisis Line.

"I thought, 'Oh my god, did I just hear that?'" Brown says.

Brown says he's learned to listen for what he calls the buffers to suicide.

"They'll say, 'If it wasn't for my religion' or 'my child' or 'my pet, 'I would kill myself,'" Brown says.

That's their firewall, he says, and it can prevent them from going through with the suicide.

The calls can last a couple of minutes or, in rescue situations, a couple of hours, Brown says. There's no time limit.

Despite tomes of research, much is still unknown about suicide and suicide prevention.

Suicide recently moved from the 11th overall cause of death among adults in the US to the 10th, Kemp says. And most experts agree that suicide rates among veterans and active service members have increased in recent years.

The high number and duration of tours may be creating risk factors for active-duty service members in Iraq and Afghanistan. Added to that is the financial stress and pressures of raising children under such transitory conditions, Kemp says.

But what's still unclear is how much the rates have increased, and why. Much of the confusion stems from the different ways suicides are reported.

There are more than 30,000 suicides in the US annually, according to a 2008 report prepared for Congress. Suicides among veterans and active service members are included in that number. Some research suggests that they may account for about 20 percent of these deaths.

But there is no suicide surveillance and reporting system specifically designed for veterans. While the Center for Disease Control collects data on suicide rates, many states are not required to report that the deceased was a veteran or active service member.

VA Director Kemp says she is concerned by the growing assertion that military service somehow increases suicide rates, and that there are precise ways of preventing it. Out of all the suicides that occur among active service members, about a third occur with people who are deployed, about a third occur among those who are home, and about a third occur among those who've never been deployed, she says.

And Vietnam-era veterans make up about a third of the suicides among all veterans, Kemp says.

Bales is a Vietnam vet, but says he liked his time in the Army.

"I was a door gunner and crew chief on helicopters," he says. "I loved flying. I loved helicopters."

He says he can't pinpoint a particular incident that caused his PTSD. He says he understands the symptoms, and how the disorder led to his struggle with alcoholism and to his suicide attempts. But he says he doesn't know when or how it happened.

"Instantly something inside of you changes and nothing is ever the same again," he says.