Pressing ahead on his skis, Ivan Castro could tell whether the snow beneath him was powdery or icy. He could hear his teammates describe the scenery – "a desert of white" – and he could feel the sun on his tent when they rested. The only thing he couldn't do was see his surroundings: the desolate flatlands of the South Pole.

A captain in the U.S. Special Forces who lost his sight after a mortar blast in Iraq in 2006, Castro was one of a dozen veterans from the Iraq and Afghanistan wars who embarked on a historic 200-mile race across Antarctica to the South Pole last winter. Split into three teams of four by nationality – American, British, and a combination of Canadians and Australians – the participating soldiers had all suffered some type of severe injury in battle. U.K. team member Duncan Slater, a former British Royal Air Force officer, is a double leg amputee. Other soldiers have prosthetic arms, struggle with post-traumatic stress disorder, or have been badly burned.

The expedition was organized by the U.K.–based group Walking with the Wounded, which assists vets with job training and education. To help raise the mission's profile, each team had a celebrity member in addition to seasoned guides: Prince Harry of Wales, a helicopter pilot in Britain's Army Air Corps, walked with the U.K. soldiers; actor Alexander Skarsgård, who served in the Swedish navy before True Blood, was on the American team; and Dominic West of The Wire (who barely trained and joked before the trip that it was evidence of? "a midlife crisis") walked with the Canadian-Australian squad.

In late November, teams arrived at the airbase in Novolazarevskaya, Antarctica. They set out with pulks – sleds loaded with supplies, which weighed as much as 200 pounds each – aiming to ski for nine hours a day, with five-minute breaks. But one week in, the race was almost derailed. Soldiers didn't take enough breaks, and the altitude (10,000 feet) led to headaches and breathing issues; three members of the Commonwealth team passed out. Therese Frentz, from the American team, was so demoralized, she almost quit. "People were overwhelmed and too tired to take care of themselves," says Inge Solheim, a guide for the Americans. "They started to make mistakes."

For Castro, the trip was particularly challenging. Following the mortar attack, he endured a collapsed lung, multiple surgeries, and 18 months of recovery. He went on to run some 30 marathons, but the South Pole tested him in ways he hadn't expected. "When you're in the military, you train for different tasks, like demolition or shooting. But the cold and altitude in Antarctica, you don't find that anywhere else," he says. "It took us out of our comfort zones." Dealing with a bad cough that made breathing difficult, he had to be driven about six miles in a support vehicle.

"That was one of the most difficult decisions of the trip," says Skarsgård, who got to know troops while filming the HBO military miniseries Generation Kill. "They're pretty determined soldiers – they're not going to give up. But when it's –35 with a heavy wind and people are pushing themselves too hard, it's really dangerous. The goal was first and foremost to get the soldiers to the South Pole together."

After nine days, the race was called off, and the trip became an all-for-one quest to reach the end. With the pressure off, the soldiers were able to focus on the most taxing terrain: frozen ridges of snow, called sastrugi, that rose as high as 5 feet. Castro's injuries acted up – he felt pain in his shoulder, back, and arthritic right hip – but he'd pop some Tylenol, blast Springsteen and Aerosmith, and drag his pulk over the frozen waves. "It was a continuous roller coaster," he says. "But we had to stay the course." In a sign of how much the teams bonded, Castro used Slater, the British double amputee, as his guide for the last six miles.

Two weeks after they'd departed, all 21 expeditioners arrived at the South Pole. Castro came away with only a bad blister and a few bruised toenails. But he and the other veterans took away something more. "Despite the conditions, we were all able to do this," he says. "We had the first blind man, first person with PTSD, and first amputee to make it to the South Pole. We wrote a little paragraph in history. We wanted to take our first step, not just in the South Pole but in life."