On a sunny afternoon in Baqubah, a convoy of Iraqi troops and U.S. soldiers depart the small base they share on a mission to bring blankets and heating oil to a nearby village. They drive down an empty road, passing packs of dogs and curbs scarred by weeks of steady roadside bombs. Suddenly, the team's humanitarian operation turns deadly as an explosion rips into the lead humvee. Sgt. Chester Jones and Sgt. Maj. Eddie Del Valle help rush a critically injured young sergeant to the field hospital. Jones, a medic, cradles the soldier's injured head as he vomits, while another helps change bandages soaked through with blood.

It is twilight as troops from the 3rd Brigade Combat Team, 1st Cavalry Division, tow the blasted humvee back to base. They cover it with a tarp, then get the news that they fear: The young soldier, Sgt. Jay Gauthreaux, has died from his wounds.

That was just over one year ago. Today, Del Valle and Jones are back home at Fort Hood, Texas, after their second Iraq deployments. Like tens of thousands of this war's veterans, they look back on their time in the country with a complex mixture of pride, frustration, satisfaction, and sadness. Del Valle recalls, for instance, the emotional task of cleaning out Gauthreaux's room the morning after the attack, packing up photos of the fallen soldier's 4-year-old son. "He's the same age as my little daughter," says Del Valle, "so you put yourself in that situation." Jones saw war's human toll every day while training Iraqi Army medics, but that didn't lessen the shock of losing his good friend. "I didn't realize it was G until I ran to the truck and pulled his body back," Jones says. "With training, you learn to try and push that stuff aside," he adds, "but it's tough."

Just as wars leave a lasting mark on soldiers, they tend to change the culture of the armies that fight them. As the fifth anniversary of the invasion of Iraq approaches, American troops are reflecting on their experiences even as they await how their mission will be judged. So, too, the institution of the military is wrestling over its own narrative for this war, assessing how well America and its commanders have used one of the most powerful tools available to any nation. The lessons it takes away from the experience of its soldiers and marines will influence how it adapts and organizes itself—and how it cares for those sent to do the nation's fighting.

What is immediately clear is that this conflict has put enormous demands on American troops. They are warriors on some days, diplomats on others, in a conflict with no clear front lines and a changing cast of adversaries. And while they are grateful that the American public has steadfastly supported them, regardless of feelings about the war itself, many soldiers report a sense of disconnection, too. America as a nation is not waging this war, many tell you—its military is.

Recent security gains in Iraq, particularly the sharp declines in combat deaths, have come as a welcome development. But there remains a heavy burden on America's fighting men and women. Commanders express grave concerns for troops shouldering wars on two fronts with no end in sight, particularly the half million who have served more than one combat tour since 2002. Soldiers in Iraq, who have seen the duration of their deployments extended as a result of an inadequate post-invasion plan, work seven days a week for 15 months straight, minus two weeks for a trip home to visit family. And they do it all, they joke, without beer (American troops today are forbidden to drink while at war). More than 60,000 troops have been subjected to controversial stop-loss measures—meaning those who have completed service commitments are forbidden to leave the military until their units return from war.

Sacrifice. The news that their yearlong tour was lengthened by three months hit the team hard, says Del Valle. "That was the worst. It's like when you're real thirsty, and you're about to reach for the bottle—and somebody pulls it far away from you." Midway through medic Jones's tour, his wife called to ask for a divorce. "I'm not mad at her, because I can't blame her," he says. "She was tired of being alone." Jones has been deployed to Iraq two of the past five years, which has left him little time to see his children, now ages 4 and 2, grow up.

The sacrifices are great, and sometimes soldiers wonder why they keep making them. On the night that Gauthreaux died, Del Valle and Capt. Christopher Whitten, the gunner that day, talked about their career choice over a game of chess at a small shop on their base as the Iraqi owner served them tea and warm bread. They express a brief moment of doubt about the extent to which what they do is really understood by most Americans. "You get in a humvee every day because that's the job that is feeding your family. I also believe in what we're doing here," says Del Valle. "Our soldiers here are giving 100 percent for every American guy back in the States." Whitten nods, adding, "It makes you wonder, does anybody really appreciate what that guy gave up today?"

It is not an uncommon question in this combat zone. Historians will tell you that wars throughout the ages, whatever their outcome, tend to wreck armies and wear out soldiers. Troops hasten to add that the belief that they are making a difference in their jobs helps mitigate the immense strain of being a soldier today. "I would argue that you haven't seen an army like this since the demise of the Roman legion—such a small number of forces able to influence the world," says Clinton Ancker III, a retired Army colonel and director of the Combined Arms Doctrine Directorate. When the 3rd Brigade Combat Team arrived in Baqubah, there was widespread corruption and heartbreaking violence against civilians. During the tour of Del Valle, Whitten, and Jones's brigade, they drove out terrorists and saw some life return to the markets, children to soccer fields. It is the sort of impact that makes a military career attractive, they say.

But the desire to make a difference can lead to even greater frustration when troops return after previous tours in Iraq to find what they consider to be little change or even backsliding during a counterinsurgency campaign in which the very definition of victory is still a lively topic of debate. That frustration can be compounded, too. Ancker argues that soldiers are under "a lot more stress" now than they were in Vietnam. "The atmosphere is more physically demanding. And in Vietnam, we were guaranteed at least a year between deployments," he says. When soldiers are injured—physically and psychologically—they are at the mercy of a deeply overburdened system that they cannot always count on to take care of them.

Camaraderie. The military has drawn lessons from past wars, notably Vietnam, reorganizing the Army into brigade combat teams in part to encourage unit cohesion and camaraderie. This has promoted the sort of psychological bonding that gives troops a sense of support in the face of the enormous demands, says Jeffrey LaFace, the division chief of the Army's Combined Armed Center.

That camaraderie is clear on forward operating bases throughout Baghdad, where troops organize flag football matches and barbecues and decompress in coffee shops and Internet cafes with fellow soldiers and marines who have become close friends over the years. "Soldiers go in as units, with the same group of guys that they have known since they were privates in Kosovo and Bosnia," says LaFace. These "adopted families," he adds, help to stem "some of the weirdness that we had coming out of Vietnam." That weirdness included soldiers who shot officers when they didn't want to do a mission and riots in U.S. military prisons overcrowded with deserters.

It is another notable legacy of the troubled Vietnam-era Army that many of today's volunteer soldiers have little desire to see the nation return to the draft. "It's the only thing that would make me get out of the Army," says Capt. Scott Hubbard, who recently returned from a tour in Iraq. The last thing you want to do, he adds, is fight next to someone who doesn't want to be next to you.

Despite the strains, the retention rate for troops in Iraq remains high, commanders point out. Their concern, though, is whether it will stay that way. "The entire Army leadership—and rightfully—we get a little nervous," says Peter Chiarelli, the military assistant to Secretary of Defense Robert Gates and until 2006 the widely admired No. 2 commander in Iraq. "All of us are extremely concerned that we could cross a line without even knowing it."

Some commanders in Iraq worry that they are flirting with those lines now as demands on soldiers show little sign of letting up. There is growing evidence that post-traumatic stress is taking a toll: The number of troops who tried to commit suicide or injure themselves increased from 350 in 2002 to 2,100 last year. So, too, can the simple fear and fatigue that accompany daily patrols. One active duty commander recalls a unit that had gone months without a serious casualty, only to have a soldier hit by a sniper weeks before the unit was scheduled to head home. The commander was approached by an officer carrying a spreadsheet that charted out the number of times company commanders had gone out on patrol or operations over a two-week period. "I had cases where I had officers who by their job nature should be going out all the time, who'd only gone out two or three times," he says. "It was probably related directly to losing soldiers, personal fear, and the fact that you're only a month or two out from going home," he continues. "I asked them, 'Have you considered the effect this has had on your soldiers?' I remember what a leadership challenge it was, and I imagine that a lot of similar things are occurring in other battalions."

Changes, challenges. Today, troops discuss such leadership challenges at countless outposts in Iraq and at the premier centers of military learning. These chats are not always pretty. Some note, for example, that Congress has fewer military veterans than in the past and, perhaps as a result, shows too much deference to the military leaders who testify on Capitol Hill. "Congress doesn't ask the tough questions they should be asking, because they're afraid that they're going to be accused of not supporting the troops," says one captain on patrol in East Baghdad. His buddy agrees. "Debates in Congress don't hurt our feelings. That's what we're here for, freedom of speech."

There is little doubt within the military itself, particularly among more junior officers, that this freedom of speech includes a growing willingness to question the decisions of commanders leading the war. That is driven in large part by the experience they are getting in the field: In today's military, the average captain has spent more time in combat than most World War II veterans—and more than some senior officers now in the military.

Indeed, military leaders acknowledge this change. "We've got to listen to the young folks—they have lived this conflict in a different way—and make sure their lessons are incorporated into this Army," Chiarelli says. "In order to do that, you've got to be willing to accept a dialogue in which many of the things that old guys like me thought are challenged."

Those challenges include new ways of thinking about how decisions are made. The Army has recently launched its own "Red Team University" to train officers to be, in essence, the opposite of yes men. Graduates of this program are then placed in brigades to question the assumptions behind decisions in hopes of averting tactical and strategic missteps. And though many argue that soldiers' grumbling about their commanders' decision is a tradition as old as the Army itself, Richard Kohn, a war historian at the University of North Carolina, believes one thing is clear: "I think that coming out of the war, you're going to have a much more candid military."

Informed support. That candor, too, must include presenting a realistic picture of the war effort to the American public, say the students at Fort Leavenworth, Kan. Not doing so in advance of the Iraq war was a mistake, they add—one that should not be repeated. "We should now consider whether we can ever successfully go to war for an extended period of time without the informed support of the American people," writes Chiarelli in a recent article for the journal Military Review.

But garnering that informed consent presents a dilemma: How does a military defined by its can-do culture paint a more realistic portrait of war? It might begin, troops say, with managing expectations—of the American people and of the soldiers themselves. "We expected to come in and throw another 3-pointer and everyone stand up and cheer," says Hubbard. "There was a lot of emotion, a lot of rhetoric, all the country music songs getting everybody fired up," he adds. "I think a lot of folks screaming for war—on both sides, political, civilians, military—just don't understand what it takes."

And that remains a cause of concern for troops today. Maj. Kareem Montague, an Iraq veteran and Harvard graduate, wonders too about the war's impact on a country in which only a small slice of its citizens are serving in the military, and how it may affect the civil-military relationship. "It's not that it's unhealthy, but it's becoming more and more separate," observes Montague, now a master's student in the prestigious School of Advanced Military Studies at the Command and General Staff College in Fort Leavenworth. "If you have fewer and fewer people who have served, you have to worry about whether you can have an intelligent conversation about how the military can best serve the country."

Ask soldiers here why they signed up, and many will say for duty, an instinctive feeling they have that you cannot be a citizen without doing this. Many others say the money is a big incentive—specifically, money for an education that they couldn't otherwise afford. "I did it for college, and because I had nowhere else to go," says one Baghdad-based soldier. Another confides that he sometimes feels like a mercenary and a "walking advertisement for one of Cheney's defense companies—like they just want us to be on TV all geared up in products." The conversation leads another soldier to privately comment later that, "The burden of this war falls disproportionately on the poor."

Faye Crawford, the mother of Sergeant Gauthreaux, wrestles with that point. She is now raising her son's 4-year-old son—he was a single father—and she says that sometimes in her darkest moments she has blamed herself for not having enough money to send her son to college. "If I could have sent him to college..." she begins, and her voice trails off as she chokes back tears. She knows, too, that her son loved what he did, and he believed that he was helping people in Iraq. "He would say, 'Mama, you should see their faces. They're so grateful.'" But Crawford wrestles with her son's sacrifice as the war fades from the front pages. "You hear that the economy is more important in the election than the war is," she says. "Sometimes I worry that people are already forgetting."

Strains. The evening that the team learned Gauthreaux had died, Del Valle contemplated getting out of the Army, imagining what his own death would do to his wife and daughter. Now home at Fort Hood since December, Del Valle, a native of Puerto Rico, has been promoted to the rank of command sergeant major. During his time in Iraq, he helped his own soldiers through some rough times and grew close to his Iraqi Army counterpart. Today, Del Valle is prepared to deploy again. "I think it would be kind of selfish for me to walk away from the Army now," he says.

The family strains on U.S. soldiers are immense, but Jones says troops are also helping another country rebuild itself and its families as well. "That matters a lot," he says. "I went over and trained a medical platoon. Those guys are really proficient now, and I'm proud about that," adds Jones, whose next assignment will be as a recruiter.