Chris Beck spent two decades serving as a Navy SEAL. He earned a Bronze Star, a Purple Heart and spent time with the exclusive Seal Team 6 – he was a war hero. But after Beck retired, he displayed a different kind of courage.

The 46-year-old man began living life as a woman. Chris became Kristin Beck – an identity that would've been rejected by the special operations force. Beck's journey is documented in “Warrior Princess,” a memoir published over the weekend, with co-author Anne Speckhard.

"For years Chris had turned off his sexuality like a light switch and lived as a warrior, consumed with the battle -- living basically asexual. For Chris the other SEALs were brothers and in the man's man warrior lifestyle, even if he had wanted to entertain sexual thoughts, there really was never any time to be thinking too much about sexuality," the book says.  

In the biography, Beck describes the struggles behind keeping his sexual identity a secret in a profession where transgender men and women are forbidden from serving. In one excerpt, Beck describes how he had to disguise himself as an Afghan man to blend in with Taliban men, who'd expressed a deep-seated hatred toward women.

"It was weird that I could grow a beard and trick them into thinking I was one of them -- and really I'm an Amazon woman in disguise as a U.S. military guy in disguise as a Pashtun!" 

After retiring in 2011, Beck began coming out as a transgender woman to family and friends online, saying "No more disguises," Speckhard said in an interview on Monday, according to the Virginian-Pilot.

Kristin Beck is now a military contractor in Tampa, Fla. She's on hormone therapy and plans to have sexual reassignment surgery. She wears long hair, make-up and women’s clothes, Speckhard told ABC News.

According to a 2011 survey by the National Gay and Lesbian Taskforce, roughly 20 percent of the American transgender population serves in the military – twice the rate of the general population. But even after “don’t ask, don’t tell” was repealed, transgender men and women are still banned from serving openly.

Some hold the ban is in place because the military considers transgender members “mentally ill,” the Huffington Post reports. Eileen M. Lainez, a spokeswoman for the Department of Defense, said "DoD regulations don't allow transgender individuals to serve in the military, based upon medical standards for military service."

One gay rights advocate believes it could take more than 10 years to change military policy toward transgender troops. Transgender troops like Jessica, who only gave her first name, said she had to conceal her female identity while serving as a Marine, struggle with making the choice between their gender identity and a career.

“Sometimes I get teary thinking about never being a ​Marine again. I want to be in for my entire career. I want to retire as a first sergeant or, hell, maybe even a sergeant major one day. I’m not done yet,” she told OutServe magazine.