A crack soldier who was an ultra-tough Navy Seal has done one of the bravest things of his life - had gender reassignment surgery to become a woman.

Chris Beck sported a beard during his 20 years in the US Army and was detailed on an assortment of deadly missions as a member of the unit that took out terrorist mastermind Osama Bin Laden in a daring raid.

But now the facial growth is gone and transgender Beck has started wearing skirts in his new life as a "warrior princess".

It is quite a change for a person steeped in the macho world of special forces soldiering and its life-or-death risks.

Now known as Kristin Beck, the former elite soldier has taken up horticulture and created a "peace garden" at her home, in St Petersburg, Florida.

Her story has been told in the autobiography, Warrior Princess.

Co-author Anne Speckhard explained how Beck was able to live a dual existence during her military career as a man.

It was simply a case of there being no time to get hung up about his conflicted identity, Speckhard said. There were always missions to complete and enemies to be targeted and destroyed.

"For years Chris had turned off his sexuality like a light switch and lived as a warrior, consumed with the battle - living basically asexually," Speckhard told ABC.

"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."

When the time came to hang up his boots and gun and leave the army, there was at last the opportunity to live life in the way he had always dreamed of.

With his new identity there was also the desire to help combat veterans as they come to terms with the scars they bear from years in the military.

Beck says on her website Healing Grounds: "Too many of my comrades are returning from the battlegrounds of Iraq and Afghanistan and do not find peace and are committing suicide.

"Sitting in my back yard or at my fishpond I no longer feel anger, resentment or depression, I feel peace. I want to give this option of a peace garden to my veteran brothers and sisters.

"We fought on the battlegrounds for freedom and the American way of life. Now it's time to be welcomed home to a Healing Ground."