As soon as Bill Krissoff glanced out the front window during breakfast to see who had rung his doorbell at eight on a Saturday morning, he knew. Three Marines, ramrod straight in their dress blues, stood next to an Army chaplain.

Nate, Krissoff's elder son, twenty-five years old, had deployed to Iraq with an elite reconnaissance battalion as a first lieutenant in the Marine Corps.

"We regret to inform you," one of the Marines began saying once Krissoff opened the door. He doesn't remember the rest. His head spinning, his body seized with shock, he stumbled through the house to wake up Christine, his wife. Soon they were sitting together on a living room sofa as the Marines explained, with grim solemnity, what had occurred a half day earlier half a world away from their home in Reno, Nevada.

Nathan M. Krissoff, a counterintelligence specialist, had been returning to his base from a village near Fallujah when his Humvee drove over a bomb buried in a dry riverbed. The brunt of the blast hit the vehicle's right side. Nate had been in the right rear seat.

The Marines sat stoically, awaiting the next question Bill or Christine would ask.

The Krissoffs wanted to call their other son, Austin, at the Marine Corps' Officer Candidates School in Quantico, Virginia.

Less than three years younger than Nate, he was following his brother's trail from an elite prep school in Pebble Beach, California, to a small New England liberal arts college, and then into military service.

The Krissoffs aren't one of those families in which every male for the last four generations has worn a uniform. Bill, who came of age during the Vietnam War, wasn't drafted and didn't volunteer. Nate hadn't been on the military track. In high school, he wrote poetry, played in the school symphony, and enjoyed wild-water kayaking. At Williams College in Massachusetts, which doesn't have an Army or Marine ROTC program, he captained the swim team and majored in political science.

Then came September 11, 2001. He was a junior. The father of his best friend on the swim team, a New York banker, did nothing for six weeks but go to funerals. Nate's carefree ways began to turn more serious. A year after he graduated, he applied for a job with the CIA. At his interview, the recruiter was impressed with Nate's education and aptitude but urged him to get some seasoning before pursuing such a career. Crestfallen, Nate contacted a friend from Williams who had become a Marine intelligence officer. If he wanted seasoning, his friend said, the Marines would give it to him.

In June 2004, as the Iraq war was becoming ever more perilous for American troops, Nate told his father that he wanted to become a Marine officer. Bill was more than a little apprehensive.

"Do you fully understand what this means?" he asked his son. "Do you understand the risk?"

Nate said he did.

Three months later, Nate was marching across the parade field at Quantico, a newly commissioned second lieutenant. Bill and Christine sat in the bleachers, as proud as the other parents, but understandably anxious. This is the real deal, Bill thought to himself as he watched his lanky son in the distance, standing at attention, his thick, dark hair shorn into a Marine-regulation high-and-tight buzz cut under his cap.

But before Nate could be called into a battle zone, there would be Basic School, where he was taught the art and science of leading Marines. Then intelligence school. Then an assignment on Okinawa. It was there that he talked his way into an Iraq deployment with the Third Reconnaissance Battalion.

As he headed to Iraq in September 2006, he sent an e-mail to his parents and Austin, who had graduated from college and was preparing to enter Marine officer school.

Almost five years to the day after September 11, 2001, I have the chance to put my money where my mouth is in terms of service ... I'm constantly reminded of that famous quote from Tom Hanks' character at the end of Saving Private Ryan: "Earn this." Earning it will mean sacrifice, determination, doing my job to the best of my ability. I chose this, and I wouldn't have it any other way. The complexities of the conflict and the shifting perceptions of the world are all but totally irrelevant to the fact that we fight for the men at our side; my success will be gauged by the responsibility to safeguard Marines and accomplish the mission, not by any other metric. I'm lucky to be deploying with such a phenomenal, savvy group of guys.

Several weeks later, Nate wrote to Austin, who had started school at Quantico, with a description of an attack that killed Sergeant Jonathan J. Simpson, a much-admired member of the recon battalion.

Why do I tell you this? Because Sgt. Simpson and many all-Americans like him are the ones you will be entrusted to lead, protect and stand in front of. Never forget that all the trials and training you and the other candidates (eventually Second Lieutenants) go through is not about you. America's sons and daughters will be entrusted to your care. You owe them competence, discipline, courage, judgment, etc. Post Sgt. Simpson's memorial picture, perhaps up on your squad bay read-board, tell your fire team and squad and platoon about him -- as a clear reminder of what this is all about. Keep it with you through the trials ahead. Because when you hear the final roll call, the long bugle playing taps, and the bagpipes wailing -- we better have done everything short of the hand of God Himself to accomplish the mission and bring Marines home. It is a sacrifice he and many like him have made fighting for each other. Earn it.

When Nate became the 2,924th American service member killed in Operation Iraqi Freedom on December 9, 2006, Austin was almost finished with officer school. He wanted to stay with his training platoon, "the only people," he thought, "who understood what happened." But the staff at Quantico put him on a flight to Reno.

His mother hoped he would reconsider his decision to be a Marine -- the service offered him the choice of walking away because he was his parents' only surviving child -- but he would not change his mind. Nate "would have wanted nothing more than for me to carry on the mission," he said. But to partly assuage his mother's concerns, he decided that instead of going into the infantry as he had planned, he would specialize in intelligence, as his brother had, though in a noncombat role. A week after he arrived in Reno, he was commissioned as an officer in a low-key swearing-in at his parents' house.

On the Saturday before Christmas, the Krissoffs held a memorial service for Nate in Reno. White-gloved Marines hoisted a flag-draped coffin containing an urn with Nate's cremated ashes. The national anthem was played. A teacher at Nate's high school recalled his warmth, his love of literature, and his mischievous side. "As a young man Nate was, indeed, Dickens' Pip, Salinger's Holden, and Twain's Huck. But he was also Ferris Bueller." A friend from Williams described him as "goofy, hilarious, and charismatic on the outside but disciplined, insightful, and focused on the inside." Captain Michael Dubrule, who had led Nate through intelligence training, told the mourners that Nate skillfully collected information to help save the lives of American troops and innocent Iraqis. "I want you all to know that Nate died doing what he loved, leading men in combat, saving lives, and making a difference in the lives of so many," Dubrule said. "No greater epitaph can be written, no greater sacrifice can be made."

After a few weeks, Bill threw himself back into his work as an orthopedic surgeon. Chris joined him in the office, where she ran the business side of his solo practice. He returned to the operating theater. Grief welled inside him, but his skill as a physician was undiminished. Soon, however, treating busted shoulders and bum knees -- as he had for twenty-eight years -- began to feel unfulfilling. One day that spring, a patient came in complaining of minor knee pain, the sort of ache that would go away with some rest or a varied workout routine.

Why, Bill thought, am I spending my time hearing people complain about nothing?

A few months later, Nate's battalion commander, Lieutenant Colonel William Seely, traveling the country to visit the parents of his fallen Marines, came to see the Krissoff family. Bill and Austin took him for a hike around Lake Tahoe's Emerald Bay, and Bill asked Seely about medical care for Marines in Iraq. Seely told him that every Marine battalion deploys with a surgeon and numerous medics, all from the Navy. As Seely described the role of the battalion surgeon, the penny dropped for Bill.

That's what I want to do, he thought. I want to be a battalion surgeon.

Bill was as lean as his boys. He stayed fit by biking, hiking, kayaking, and skiing. He figured he could meet the military's physical requirements, so he called up a Navy recruiter in San Francisco and offered up his services. The recruiter posed a series of questions. Finally, he asked how old Bill was.

"Sixty," Bill said.

"Um, that's a problem," the recruiter replied. "You're too old." Anyone over forty-two who wants to join the Navy Reserve medical corps needs an age waiver, the recruiter explained. He wasn't optimistic about the possibility of a sixty-year-old obtaining one.

Undeterred, Krissoff called an Air Force recruiter. He got a similar answer. So he went back to treating sore knees.

That August, he and Christine received a voice-mail message from a White House aide inviting them to meet with President George W. Bush after he spoke to an American Legion convention in Reno the following week. They attended the speech with Austin, standing in the back and laughing at the president's self-deprecating humor. As the president was concluding his remarks, they were ushered into a small room with several other families. All of them were "gold star" parents and siblings, those who had lost sons or daughters, brothers or sisters, in Iraq or Afghanistan.

Bush strode in a few minutes later and shook everyone's hand. He spoke at length about the war, explaining his strategy and lauding the sacrifice of his audience's fallen relatives. The Krissoffs listened intently. Iraq was being torn apart by a civil war. U.S. troops were getting attacked daily. Hundreds of Americans had come back in caskets since Nate's final journey home. The war had become deeply unpopular: fewer than four in ten Americans still believed it was worth fighting. When Bush asked for questions or comments, Bill spoke up. He knew what had driven Nate to join the Marines, to find his way to Iraq. He didn't want his son to have died in vain.

"Let's stay the course," he told the president.

Bush approached each family individually and asked if there was anything he could do to help them. Several made small requests for assistance in dealing with death-benefits paperwork. An aide dutifully jotted notes.

Then Bush walked over to the Krissoffs and posed the same question.

"Yes, sir. There is one thing," Bill said. "I want to join the Navy medical corps and serve, but they told me I was too old. No disrespect, but I'm younger than you are."

Bush's eyes widened. He looked at Christine.

"What does Mom think?"

Christine said she and Bill had talked about his desire to serve.

She wasn't thrilled with the prospect of his traveling to a war zone, but she wouldn't stand in the way if going might help her husband heal. "I'm on board with it," she said.

Bush turned to Austin, who had driven up from Camp Pendleton to accompany his parents to the meeting. He was skeptical, but he, too, didn't want to sabotage his father's quest. "He'll be pretty good out there," he told the president.

Bush said he would be meeting with General Peter Pace, the chairman of the Joint Chiefs of Staff, in two days and would mention Krissoff's request. He summoned Karl Rove, one of his top aides, to collect the necessary information from Bill.

"I'll see what I can do," Bush said.

Three days after meeting Bush, Krissoff received a phone call from the same Navy recruiter who had scoffed at his request to join a few months earlier. "I have orders to meet with you by the end of the day," the recruiter said. When Krissoff replied that he was trailering a horse with his wife and could not immediately drive down to San Francisco -- three hours away by car -- the recruiter was undeterred. "I'm coming up to see you," he said.

Krissoff took the recruiter to dinner, filled out a stack of paperwork -- and waited. A month later, he got word that he had been accepted into the Navy Reserve for his dream assignment: a Marine Corps medical battalion.

Although he was required to train once a month, Krissoff treated his reserve duties as a full-time job. For him, joining the military wasn't about wearing a uniform and attending to Marines on the home front. He wanted to go to Iraq, as Nate had done and Austin would be doing soon. And that meant spending as much time as possible learning how to be a combat physician. He had decades of medical experience, but none of that involved treating blast wounds.

He and his wife moved to the San Diego area in early 2008 so he could be closer to the Navy hospital on the Marine Corps air base in Miramar, where he signed up for every combat-medicine course he could take. He traveled to Morocco that summer to participate in a military exercise during which he practiced working in a field hospital. He attended advanced workshops at an Army hospital in Texas, and he joined Marines on heart-thumping hikes through the rocky Southern California hills to prove to superiors a generation younger that he could withstand the rigors of deployment.

When his training felt grueling, he thought back to a letter Nate had written while he was at officer school:

0 dark 30. 4:30 a.m. Then it began. Platoon staff formally introduced us and then took charge. Imagine tables flipping, chairs getting thrown against walls, instructors screaming. A volume that shocks the body. PT has been harder than any work I've done in my life ... Pain is constant here. Honor, sacrifice, integrity aren't just fairytale phrases. They're earned every day in sweat, tears, blood, etc., by these people. The values of the USMC are one of a kind. Keep shit straight ... The more you sweat in peace, the less you bleed in war.

Austin, who was stationed at Pendleton at the time, came by to watch his father put on his uniform. "He'd shake his head and redo everything," Bill said with a chuckle.