The US marine Corporal Steven Schulz, 22, talks softly and quickly as a result of his brain injury. His mother, Debbie, is sitting next to him and tells him to slow down. He nods, just a little bit embarrassed.

In April 2005, five months into his second tour in Iraq, Steven was with five comrades in a military vehicle when an improvised explosive device (IED), a home-made bomb, detonated. He took the full force of the blast through his window, causing severe head injuries. The marine behind him got a mild concussion. Nobody else in the vehicle was hurt. Steven was 20.

He doesn't come from a military family. He was born in Austin, Texas, and raised in a suburb of Houston, which is where he graduated from high school. He went to a community college in Austin for one term before joining the marines.

Debbie was teaching at a local high school at the time of the injury, but has given up her job to be with Steven through the arduous process of rebuilding his body and rehabilitating his life - as far as is possible.

They are at the National Naval Medical Center (NNMC) in Bethesda, Maryland. Built by Roosevelt in 1940, it's where JFK's autopsy was carried out and where today, surgeons and medical teams are working miracles with bodies and minds fragmented in Iraq. Many are barely alive when they arrive, some having died and been revived several times en route from the front.

In the 18 months since his injuries, Steven and his family have been shuttled back and forth from one medical team and facility to another, for 14 operations. The military covered some expenses: hotel bills and air fares for up to three family members are paid; and non-profit organisations and veteran support groups help too.

In February 2003, when Steven first went home and told his mother he'd joined the marines, she was concerned. "I told him he was crazy and tried to talk him out of it.

We weren't at war yet, but it was looking pretty imminent." But the marines were the hardest, which is what appealed to Steven. "I knew if we went to war with Iraq it would be a ground war and the marines would be first," Debbie says.

After his injury, Steven was taken to a combat-support hospital in Baghdad, where neurosurgeons removed a large portion of skull to give his brain room to swell. They implanted the bone under tissue in his abdomen, hoping that it could be reinstated later. They got him from Baghdad to Bethesda within 72 hours. His prognosis was grim.

When he arrived, Debbie asked his neurosurgeon, Dr Rocco Armonda, the director of neurocritical care, what his chances were. He gave Steven 50%. Steven gave his mother a thumbs-up, but then the next day he had a massive haemorrhage and his chances slumped to 30%. "After that I stopped asking," Debbie says.

Steven is alert and smiles. He is hesitant to make eye contact; his left knee bounces up and down until he holds it still for a few seconds and it stops. The involuntary tic and the shyness are both part of the injury to his right frontal lobe. His left arm and left side are still profoundly weak and he can't walk by himself. When he speaks, his voice is flat and lacks intonation, and his expressed emotion has been neutralised. His mother worries about his ability to interact with girls. Debbie shows me a photo in her wallet. It is a snapshot from when Steven was missing part of his skull, taken at a restaurant in Florida. What's striking, aside from the fact that it shows Steven with only part of his head, is that he is smiling. Everyone looks so cheerful. She carries it as a reminder of how far he's come.

"There were times when I would flex the muscles in my cheek and you could see the brain flex too," he says. And now? "I see myself as I've always been."

Before the reconstruction he felt abnormal. People would look. Cranioplasty has re-created his skull. It is a precise implant that is made out of plastic and putty. It is a perfect fit. There is still a slight depression near his right temple, but it is not immediately obvious. They can take fat from his belly to fix it, but Steven is putting that off for now because he needs eye surgery - the right eye still has shrapnel in it. He has had two attempts to reattach the retina. His vision cannot be corrected, but with future eye treatment and transplants, and with medical advancements, you never know what may be possible - hence the efforts to preserve the optic nerve.

When he was first injured he was anxious to get out of the hospital so that he could go back to Iraq, unaware of the damage done to him. He missed his fellow marines. Before the injury, Steven was always on the go: he loved fast cars - he wanted to be a racing driver - and, naturally, girls. An average 20-year-old alpha male.

When Steven's mother begins talking to someone else for a moment, he turns the conversation to sex. A recent trip to California to see his marine buddies was a chance to feel part of the group again. A flirtatious side emerges. He makes eye contact. He tells me he felt natural having sex. He whispers: "With two girls. Strippers. It was really great." Debbie tunes back in. She asks what he's been talking about and I tell her she doesn't want to know. She knows. "Just remember, you don't want your grandmother reading about this, Steven. It's bad enough your mother knows." The exchange between them is endearing.

"Part of the brain injury is that whatever he thinks, he says," she explains. Steven still thinks about sex a lot. That part of the brain isn't damaged. He had a girlfriend but since the injury she stopped calling.

It's been 18 months since the injury, and he is still in the marines - on medical leave. When I ask what he misses most, his voice gets even softer so his mum doesn't hear. "To be honest, it's probably to make sweet love every night to a beautiful lady." She hears him anyway: "Oh, Steven! How about going back to driving a car?"

Steven is getting tired now. He yawns, something his mum mentions never happened before - or at least not in the middle of the day. Everything is now measured in before and after, and even a yawn is observed.

"I feel you can't really look back," Debbie says. "You have to move forward. At one point he told me, 'You know, Mom, I need to apologise to you for ever joining the marines.' He felt strongly the marines were what he needed to do. He said, 'Mom, I need discipline in my life.'" She reaches over and smoothes her son's hair. "Well he got that. And he'll need it for this injury."

At the NNMC in Bethesda, surgeons are pushing the boundaries of surgery. The marines they are working on have wounds from Iraq that have never been seen. The injuries are infected and they are severe. The lessons learnt are unique to this theatre and this war. They cannot clean these wounds as quickly as in Vietnam or Korea, where bullets and shrapnel did the damage. In Iraq the weapons are IEDs - dirty, clever, deadly and sophisticated in multiple ways. It's not just the metal that eviscerates.

When an IED goes off, the shock wave can burst an intestine. The heat and smoke burns and blinds. The soldiers are also thrown into the air - so there are broken bones.

Even the soil and water in Iraq carry a virulent strain of bacteria. Acinetobacter is resistant to most common antibiotics and, if left untreated, can lead to pneumonia, fever and septicaemia. It has been identified in more than 240 military personnel in the US since 2003, killing five; and in British troops too.

The injuries that are seen at Bethesda are usually multiple-limb, abdominal, back and head injuries - all at once. They are the hallmark of the Iraqi insurgents' favoured IEDs. The war in Iraq is largely an extremity-injury war: 70-80% are arms and legs. And facial. The damage surgeons are seeing is so massive that in past wars the casualties wouldn't have survived - the surgeons wouldn't have felt equipped to save them. But new techniques and battlefield triage have helped them to react to the fresh challenges thrown up in Iraq. In this war, there are more casualties and fewer body bags - more are surviving. The total military wounded in action for Operation Iraqi Freedom from March 2003 to September 2006 is 19, 945. Out of those, 6,390 are marines.

Why are they surviving injuries that would have killed them 10 years ago? First, body armour, second, more efficient combat-support hospitals where, in under an hour after their injury, a soldier is on the table. It's no longer the stuff of MASH, plugging bulletholes and stemming blood loss. Neurosurgeons staff field hospitals now.

And specially equipped casevac (casualty evacuation) vehicles get them to surgeons faster.

Dr Maria Mouratidis, a neuropsychologist and head of the traumatic-stress-and-brain-injury programme at Bethesda, emphasises that the patients have to be looked at with "fresh eyes". It is not the same as in Vietnam: the soldiers today are not as bitter. "There are few pity parties. They are processing what they've been through, but wanting to move on," she says. There is huge emphasis on their emotional recovery, and Mouratidis reiterates the value of reconstructing physical appearance and therefore Bethesda's cutting-edge plastic surgery. But because of their injuries and traumas, their values and priorities have shifted. Physical appearance may not be as important as the quality of life they are left with.

But what of denial, depression, and the anger that comes with physical and mental damage? Maybe it's the marine training they go through. And the ability to block out the negative at all costs, and focus only on the goal. "There is a normalisation process that takes place," Mouratidis says, explaining what Christopher Malone, a marine who has lost his leg, will deal with. "He knows lots of other guys this has happened to, and they run marathons with a prosthetic leg and lead a normal life." What she is saying is this: if a soldier lost his leg in a car accident, the emotional recuperation would have been difficult. He would be more isolated. But there are lots of guys from Iraq he knows who have lost legs. "Being with others like him helps him to heal and adjust."

There are so many patients, there is strength in numbers. Anger is not productive. The objective is to heal, to get strong, to repair the damage - it's a target and targets are familiar territory. Questions: will I ever have another girlfriend? Will I ever walk again? They are batted away. Negativity is the enemy. They are being rebuilt and fixed on the outside. But will they remain broken on the inside?

On September 12, 2004, Sergeant Todd Herman, then 24, was riding in a light armoured vehicle. He had been in Iraq for seven months and was two weeks away from going home. It was his second deployment. He was heading south - two miles off base - when an IED detonated 300 yards away. He happened to catch a piece of it. A large piece of shrapnel tore into the right side of his face and took out most of it - including the roof of his mouth and his nose.

"I put my hand up on my face and couldn't tell what was what. So I just dropped down beside the vehicle - I didn't feel anything at first. But after 30 seconds my jaw started aching." His eyes are a penetrating blue and betray no signs of damage. He can see only the big E on the eye chart with his left eye and it can't be corrected.

His smile is crooked, but he smiles frequently and without self-consciousness. He is proud, calm and polite - hands folded in his lap when he speaks, and when he stands he is tall, muscular and, as one woman nearby observes, "hunky".

"A doctor from one of the other vehicles started wrapping me up," he explains, "and then they did a tracheotomy on me because I had a hard time breathing. My ripped palate had blocked off my airway." He pauses. "I figured it was probably going to be a long ride back. On the way back to the medical cache after it happened, I heard my buddy whisper to the doc, 'You know his nose is detached,' and I thought, 'Wow, that kind of sucks.'"

It took a while to get him into surgery because it was backed up that day, and he remembers the nurses standing beside him, holding his arm and talking to him. After surgery in Baghdad, he was flown to a military hospital in Germany for three days and then to Bethesda.

Todd is from a small town in Pennsylvania called Coalport, a former boom town for coal miners. He is an only child whose parents are divorced, but they are still a close-knit family - brought even closer by what has happened. When Todd got out of high school he worked for a couple of years refabricating train components, but he wanted a challenge. His father was a marine and Todd decided to enlist "to see the world". Other than Niagara Falls on a class trip, he had never been anywhere. He knew there was a good possibility that he would be sent to Iraq, but it didn't deter him.

The politics of the war he was fighting are not beyond him. When asked, he is thoughtful before answering. "I think politics - pardon my French - are a bunch of bullshit. Politics take place in everything. From work to government and religion. Did I vote for Bush?" There is a long silence. "I think he's doing the best job he can. Do I think that he's the best president for the United States? No, I don't. Do I think he's a bad guy? Probably not.

"I don't know him personally, and I'm sure there are things behind the scenes that take place that we'll never see or know about, so I can't make any type of real judgment without knowing the real deal and no one's ever going to know the real deal. You know what I'm saying?"

The Navy captain David Bitonti, head of oral and maxillofacial reconstructive surgery, shows the "before" photos of Todd's injuries and describes the challenge. His right cheek was gone. Where does the tissue to restore it come from? You can't pull the skin down - it will take the eye with it. Can't pull it up - his mouth will be crooked. Can't use skin from his body, because he doesn't want him having to shave underneath his eyes. And how to replace Todd's freckles? It is all about looking normal. Todd's face had expanded - one eye was moved far over to the right and hung lower. There was a missing orbital wall on the left side. His upper jaw was detached. They had to rebuild most of it; 3-D models are built to ensure a "custom fit". This is new. The models are made with a scan on a computer, which in turn "instructs" a modelling machine, and the result is uncanny; the pieces fit like a puzzle.

In Todd's face, bone plates from his ribs act as scaffolding. He has a tissue expander in the right side of his cheek. It's like a balloon that gets slowly filled with salt water and stretches the skin out. They wanted to make room for soft tissue. He had lost all facial muscle in and around the cheek. That had to be fixed too. "We're the experts now," Dr Bitonti says, referring to this type of reconstruction. "No one really sees this stuff but us. In every war there are unique sets of injuries."

Here is what Todd has in his face now: a piece of his skull; titanium in an eye socket; a fat-graft from his stomach; and two pieces of cartilage and bone from his ribcage bolstering his new nose. So far he has undergone seven reconstructive surgeries to repair both the structural and aesthetic damage. He was due to receive his final surgery on October 31, to straighten his new nose. After that, Todd will go through the medical boards to be discharged and he plans on getting out of the corps.

It's time to move on. He might go back to school or become a mechanic, because he likes working with his hands.

He struggles to explain how the injury has changed him. He mentions the sensory things. Things don't smell the way they are supposed to, which affects his sense of taste as well. And then there is the mirror - he doesn't see the same face. He's not used to it yet. His nose is wider and bigger. He tells me he feels no regret, but his altered appearance can't be overlooked. His self-esteem is still intact, though. Having lived through the experience, he says, he feels there is now nothing he can't get through: "It's who I am now. What can you do? Every once in a while you say, 'Man, it would be nice to look like my old self again,' but I can't dwell on it. It pops in my head, yeah, but I think, 'These are my scars. I'll wear them proudly.' It could be worse. A lot worse." It almost was for Staff Sergeant Bryan Trusty.

Bryan Trusty, 22, died four times. The first time he "coded" - when a heart stops beating - was on the plane to the US. Again at Andrews air-force base. A third time, when he got to Bethesda and the fourth, later that night. The doctors got him stable. He was in intensive care for six weeks - 95 times out of 100, someone with his injuries would be dead now. Mortar shrapnel to the brainstem and both lobes of his brain, and other severe head injuries, have necessitated extensive plastic surgery and neurosurgery. He has exceeded all expectations for recovery, though most of his childhood memories are gone and his short-term memory is nonexistent. It takes him a while to articulate. There are a few scars on his head above his forehead, but when his hair gets long, they won't be noticeable. If you didn't know his story, it would be impossible to detect his injuries.

Bryan grew up in Indiana. His family still lives there and he has an older brother who is in the navy. Bryan signed up in July 2002. He says he had no fear about going to Iraq, no thoughts about getting wounded. "I thought I'd do my time over there and come back." Today he is dressed in full uniform. He sits down, back straight, knees together, and freshly polished shoes glisten while he slowly spins his white cap around on his lap.

In February this year, his second deployment, his time in Iraq was up. He'd been there for six months, but he volunteered to extend for another four months because they needed more help. On the day he got hurt in April, he was on outside security duty at the notorious Abu Ghraib prison. He started at 5am and he got off at 5pm. He went back to base, got some food, and he and a friend were walking when mortars hit. "It was the strongest attack against the base since the war started, and we hopped into the truck with my squad to secure the base along the east wall." He got to his position and saw a car bomb hit one of the towers, so he took off running - bullets flying past, rockets bursting in the air. When Bryan got to the tower, he ran up the three storeys. Despite being hit, the tower was still standing, and he had to see who needed assistance. When he reached the top, everybody was fine.

"We picked up machineguns and started firing back. They were on top of us, throwing grenades and shooting RPGs. They were 50 yards away - I could see their faces as they were returning fire." A rocket exploded inside the tower. "It hit where all of us were sitting. There were about five of us in there. The other guy lost his eye." Bryan remembers everything in slow motion, hearing "Incoming!" and white hot metal flying in the air. He thinks the explosion blew his helmet off because he wasn't wearing it when he regained consciousness.

All kinds of metal had peppered his head. Someone had to pick him up. He couldn't walk or move any part of his body except for his eyes. They carried him out - into the blast of a grenade and more shrapnel hit him in his leg and back. A piece of it had gone through his cheek, and there is the tiniest of scars. But the velocity of the shrapnel ripped through his carotid artery and stopped near the brainstem. Death from rapid blood loss was seconds away. Bryan doesn't really want to talk about what happened to him when he coded. "It's too much to talk about it in one day. A lot of things happen when you die. What's the right life to lead - that type of stuff."

Bryan's skull was fractured and his forehead had to be reconstructed. Dr Armonda, the attending neurosurgeon who also treated Steven Schulz, sits in his office surrounded by 3-D resin models of patients' skulls. An army lieutenant colonel, he was in Iraq for a year - from March 2003 to February 2004 - at a field hospital south of Falluja, west of the Euphrates. His neuro-team referred to themselves as the "Skull Crackers". He explains Bryan's injury. To get to the ruptured artery and repair it, they inserted a catheter through his groin. Then an acrylic plate was placed in his forehead. The shrapnel near the brainstem is still there, too critical to get at without risk. He gets checked regularly to make sure it doesn't move. If it does, he could be paralysed. "It doesn't bother me," Bryan says, "except for the headaches.

And the worry. So I try not to think about it." He never worried before. That's the most significant change in his personality. He asks "What if?" now. What if the shrapnel moves? "If I go swimming, or from a car wreck, if someone rear-ends me. That worries me. Or if I fall down the stairs and hit my head."

He doesn't plan to stay in the military. He worries he'd have to compete with someone fresh from boot camp. "Jobs in the military are competitive - just like jobs in the civilian world," he explains. He's not sure what he'll do. Maybe computers or law enforcement. He doesn't regret anything. "If I hadn't got injured, I wouldn't have come [to Bethesda] and met the people I've met. I wouldn't have met my beautiful wife." Bryan was married two weeks ago to Liana, who looks at him adoringly. They met in May at a bar not far from the hospital. "You can't plan for what's going to happen tomorrow. It's going to happen. You have to roll with the punches."

It's not just the soldiers who are heroes. Dr Anand Kumar, 35, is lauded at NNMC. He is updating and creating new surgeries for the exceptional wounds he sees. "When you remove a body part, people grieve. The core idea of reconstructive surgery is to salvage - to reconstitute and improve the self-image of the patient. The other component is function. Once they are up and walking, then we work on the aesthetics."

On Corporal Christopher Malone, he has created a new surgery based on an old-fashioned technique. Christopher suffered a devastating injury from an IED. When he arrived at Bethesda, he was critical. It's life before limb in the triage sequence. He had both legs, but his right leg was so badly injured - and there was so much infection (grass and parts of his uniform blasted into lower parts of his leg) - that they weren't able to save it. In addition, he had multiple broken bones. To get rid of the source of severe infection, they had to amputate the leg, but the orthopaedic surgeons were asking: "What are we going to do about the other leg?" - he was missing a huge amount of flesh on it. Most of the skin had been stripped and tendons exposed.

Kumar had an answer: " Why don't we sew the legs together?" In effect, skin that remained attached to the amputated stump was sewn to the heavily damaged leg, to grow new blood vessels, muscle and skin to be recycled later in reconstruction of the remaining limb. He had never done this before. The principles had their origin in the 15th century, when duellists who lost the tips of their noses in a sword fight would take skin from the arm to rebuild the nose.

Kumar says: "Christopher is very easy-going, which is why he's willing to try this extreme measure. Some people are psychologically not ready to handle it." The principles for Christopher's surgery have been used on a number of casualties. "If you look back through any plastic-surgery textbook, it's the wars that have driven the specialty. Every time there has been a war, more complex procedures are invented." He explains he is in a unique position because, although these guys have devastating blast injuries, they are also in incredibly healthy shape. "It's a far different patient population than, let's say, a 65-year-old patient with cancer who has kidney damage. I have the privilege of operating on an 18-year-old US marine who, on a good day, runs with a 100lb pack for miles. That's why they can survive. And then I can put them through huge operations.

"It's one of the best operating experiences of my life, and probably will be the best work I'll have done in my career. But at the same time, the circumstances in which I have to do this are horrid. You try to fixate on fixing the problem." Kumar tries to detach. "I suppose it's a bit emotionally immature, but then again," he smiles, "I'm a surgeon." There are days when he gets "bent out of shape" but he says: "You've got to motor through. You've got to suck it up and fix these guys. But I'm superficial like everyone else. I have a Porsche." He laughs. "I'm a plastic surgeon!"

Kumar can have up to eight cases a week. It goes in waves. His caseload depends on military activity. "Are there days I'm angry? Absolutely - when you see so many people with life-altering injuries. I can't imagine all the sacrifice for nothing. Part of what gets me the most frightened is to think that we did all of this for nothing.

"I absolutely believe in what we're doing. Because the flip side is, 'Oh my God! We're doing all this for nothing?' That scares me to death. I've got to believe the sacrifices I'm seeing are for something. My job here isn't to play politics. I exercise my rights and what I think about the war on polling day, when I vote. But when I'm here, my job is to rebuild what's been broken."

Christopher Malone, 21, is in his hospital bed with the skin flap from his amputated right leg sewn to his left. He explains his tattoos. There is a dragon of power, a tree of life and petals falling for friends he's lost. There are seven petals.

Christopher was born and raised in Amarillo, Texas. And as soon as rehab is over, he plans to move back there with his one-month-old daughter and his fiancé. They can't visit yet because of the infection he picked up from Iraq. He hasn't held his newborn baby. "I enjoy being a marine. It's not all about being clean-shaven and haircuts. We have fun. We do everything together. When one of the guys gets hurt, it doesn't affect one person, it affects everyone."

He speaks quietly now because he is 40% deaf in his left ear, but his mum, Bobby Jo, who is in his room and has been at his bedside since he was admitted, says he was always low key. Her job is to make sure all her son has to think about is games and movies and what he's going to eat. She tries to keep him upbeat. She doesn't want anything to depress him or get in the way of his recovery.

The injury happened when Christopher was driving a truck that carried a grenade launcher. This was his second time in Iraq. He says he took a direct RPG attack to his door. "I was screaming at the top of my lungs. The RPG hit the fire extinguisher, which was good news, or I'd be pretty much roasted. But I got a blue mist all over me - so I looked like a Smurf." It hit his leg and his bottom. He knew that he had shrapnel in his thighs. "I was not in pain - maybe it was the adrenaline. But I knew my right leg was crushed."

Amazingly, Christopher managed to drive the vehicle and his passengers off the road to safety. He was given morphine and they put on a tourniquet to stop the bleeding. They got him to the combat-zone hospital in 12 minutes. After that he was flown to Germany. He looks over at his mother. "Mom, do you know where I flat-lined?" "Here," she says, referring to Bethesda. "Twice." "Mom, do you know when?" She tells him his second day. "Was that in my coma?" She nods. Christopher was in a coma for about a week. He arrived on August 8, 2006.

"This is just another step in my life. The only positive thing I can say is that I will get a prosthetic leg and I will walk again. I have no reason to be angry. I'm still alive." He says he will miss kick-boxing, then adds: "But after two years, you never know." When asked if he's been depressed, he looks puzzled. "No. I have nothing to be depressed about. If I start feeling depressed I won't be able to get better. I won't be able to focus on going to rehab and walking.

"I have nothing to regret. I'll be able to drive and ride a horse." He nods to his mother: "She raised me to be strong." The look on his face brightens when Dr Kumar comes up. "He has amazed me. He took a chance with me." He pulls down the blanket and shows what's been done. "First I thought, 'Whoa, this is some sci-fi stuff.' And I asked if it had ever been done before and he said no. And I'm like, 'Do you think you can do it?' And he's like, 'Yeah.' And I said, 'All right!'"

When Christopher dreams at night, he doesn't dream about walking. His dreams are about getting in a fast car and doing burnouts. But he immediately acknowledges the reality of the situation. "I know I don't have my leg any more," he says. "I'm just an ordinary guy that got hurt."

He is looking forward to the surgery. Without it, he'd have needed several skin grafts from his thighs and stomach to cover up the missing skin on his remaining leg, and they could not have guaranteed it would have been successful, necessitating perhaps a second amputation.

Now the look of the leg he keeps will appear more normal. There will be just a scar when it's done. Christopher smiles sweetly. "This injury, it's something I've got to deal with. But I will walk again. I have nothing to be depressed about because I want to get better. And the angry part? "They were doing to me what we're doing to them. It's war. And people do get hurt. On both sides. I chose to be a marine. And this is one of the things that you take with it. I still am a marine. And I will continue to be one."