While promoting the movie"Battleship"in Tokyo last month,U.S. ArmyCol. Greg Gadson found himself face-to-face with a stunned reporter.

"He thought I was computer-generated," said Gadson, a burly former West Point football player who walks with the aid of futuristic-looking titanium prosthetics. "He thought my legs were movie magic."

There was no CGI needed for Gadson's performance as a wounded combat veteran in "Battleship" — both of his legs were amputated above the knee after he was injured by a roadside bomb in Iraq in 2007. "Battleship" director Peter Berg cast Gadson in the movie, which opened in Los Angeles last Friday, after seeing an imposing photograph of the soldier in a National Geographic article about advances in artificial limbs.

Berg also enlisted dozens of other wounded soldiers as extras in "Battleship," which stars Taylor Kitsch and Rihanna as a Naval lieutenant and petty officer whose ship becomes embroiled in an alien attack. Gadson plays Mick, a double amputee struggling through his first rehab session with a physical therapist (Brooklyn Decker) when the extraterrestrials arrive.

"I believe we don't do enough to respect our veterans," said Berg, who shot one sequence of the film at the Center for the Intrepid, a facility in San Antonio that treats amputees and burn victims who have returned from Iraq and Afghanistan. "And we tend to outright ignore the people who've been seriously hurt."

Gadson, 46, has had 22 surgeries and since 2010 has been directing the Army's Wounded Warrior Program, which assists severely injured soldiers and their families. But his first acting role brought new physical and mental demands — in "Battleship," he climbs a mountain, grapples with some aliens and defeatedly tells Decker's character, "I am only half a man, and half a man ain't enough to be a soldier."

To deliver the performance, Gadson, who said he weighs about 230 pounds, had to learn to maneuver on rough terrain for the first time since losing his legs. Unaccustomed to walking or standing for long periods, Gadson fell multiple times during his more than six weeks of filming.

"When Pete called Greg, they didn't really have a conversation about, 'What's your mobility?'" said "Battleship" producer Sarah Aubrey. "Greg was very trusting and very excited by the amount of physicality and pushing himself that Pete had in mind."

Gadson said he relied on his background as an athlete to grind through the bodily challenges, but meetings with acting coaches who encouraged him to express himself brought more unfamiliar tests.

"As someone who's been in the Army for the last 24 years, we've been taught to manage our emotions and remain calm," Gadson said. "I had gotten pretty good at controlling my emotions. All of a sudden now these guys are asking me to open those cabinets that I keep locked."

Gadson has been adjusting to life in the public eye for a few years now — in 2007, New York Giants assistant coach Mike Sullivan, who had played football with Gadson at West Point, invited his old teammate to a game. Gadson, then in a wheelchair, delivered an emotional speech to the team, which had lost its first two outings of the season. The Giants went on to win that game and ultimately won the Super Bowl.

Gadson's relationship with the Giants inspired a flurry of news stories, but the father of two said he was still a little nervous about the exposure that has come with participating in a major studio movie.

"It's like, OK, am I ready for this kind of attention?" said Gadson, who will also assume new off-screen responsibilities in June as a garrison commander at Ft. Belvoir in Virginia. "Those would be the questions I would ask myself. That, and do I look fat?"

rebecca.keegan@latimes.com