SYDNEY, Australia — IT was 2 a.m., just a few days before Christmas, in a remote part of Afghanistan. Eight hours into a 16-hour shift, Ryan, a 23-year-old American naval sailor, was standing tense and alert, watching the footage of soldiers undertaking a nearby mission on a screen in front of him.

Suddenly, a hand clapped onto his back. Wheeling around to look at the face of his senior officer, Ryan knew the moment he had feared had come: His superiors had found out that his enlisted paperwork described him as female. Within three hours, he was on a plane.

Ryan, who is now stationed on a base in the United States awaiting a potential discharge, recently described that day to me. Ryan is the name his mother would have given him if he had been identified as male at birth. He does not want to reveal his real name because his case is being processed by the military.

While the repeal of “don’t ask, don’t tell” in 2011 meant gays and lesbians could serve openly in the American military, transgender people still cannot, because the military defines gender nonconformity as a psychological disorder. So transgender soldiers serve in silence, facing dismissal if exposed.

This isn’t the case in other countries. At least 12 now officially allow transgender individuals to serve openly in their defense forces. Britain has allowed transgender people to serve openly since 1999, and Australia since 2010.

The flags of these countries had hung above Ryan’s control station in Afghanistan. “I wear an American uniform and I represent a country supposedly defined by liberty and equality,” he told me. But “my allies are welcome to serve in a way that has most certainly just cost me my livelihood. If these countries’ soldiers, sailors, airmen and marines can serve openly and authentically as transgender women and men, why can’t I?”

Nine percent of transgender people who have served in the American military report being discharged because of being transgender or gender nonconforming. Almost all of the rest stay quiet for fear of harassment or abuse.

A Harvard study published last year found that most transgender military personnel in America are white, educated and middle-aged. And most eventually transitioned from male to female. It also found that 20 percent of transgender people had served in the military — double the rate of the general population. (There is a theory that many seek “hypermasculine” experiences to suppress their desire to be female.) A University of California survey found almost all — 97 percent — were not able to transition until after they left the service.

But there’s a shift happening. According to data from the Department of Veterans Affairs, the number of veterans seeking advice on transgender issues has doubled in the past 10 years. And hundreds of currently serving transgender members of the armed forces have joined an underground support movement called SPART*A. (About 20 of them are out to their peers, and a handful are also out to their superiors. They describe meeting with wildly varying degrees of support, much as gays and lesbians found before the repeal of “don’t ask, don’t tell.”)

Transgender men and women are not banned from serving by congressional law, but by military medical codes. These codes classify being transgender as a psychological disorder, which was in line with the Diagnostic and Statistical Manual of Mental Disorders III, published in 1980. But the latest edition of the manual, the D.S.M.-5, released last May, replaced “Gender Identity Disorder” with “gender dysphoria.” The point of the change, according to the American Psychiatric Association, was to make it clear that “gender nonconformity is not in itself a mental disorder.”

The military has not acknowledged this shift. Asked if the Defense Department would reconsider its policies and make the necessary regulatory change, a spokesman for the Pentagon, Lt. Cmdr. Nate Christensen, responded, “Department of Defense regulations don’t allow transgender individuals to serve in the U.S. military, based upon medical standards for military service.”

So the global anomalies remain. And a growing number are asking why.

A new documentary series called “TransMilitary,” which is scheduled to be released online in the fall, will contrast the experiences of transgender people in the armed forces in America and Britain. Fiona Dawson, the show’s host and producer, says the difference between the countries is “shocking.” While she has found several transgender members of the armed forces under investigation in America with likely discharge, in Britain, she found support, and some celebration.

“A captain in the British Army even had a ‘patch party’ thrown for her to celebrate her first day of hormones,” she told me. “Her colleagues slapped Band-Aids on their arms while she applied her first hormone patch. These are the human interactions that build a trusting, cohesive and robust team.”

Across the world, bold transgender men and women are stepping into the public light to show it is possible to live authentic lives while serving their countries. Many face rejection, many struggle with suicidal thoughts, and the great majority serve in secret. But others are speaking out.

Allyson Robinson, now an L.G.B.T. consultant, served in the United States Army and was ordained as a Baptist minister before coming out as transgender and transitioning to female. She says her greatest struggle when studying at West Point was the honor code — “a cadet will not lie, cheat, steal or tolerate those who do.” Having to conceal her true gender identity felt like a violation of that code.

But since transitioning, she says she has experienced “nothing but respect” from people in the military. Once, when she told a puzzled cadet at the West Point gate that she had studied there, he clicked his heels and said: “Well, then, welcome home, ma’am.” She cried all the way to the parking lot, and cries when retelling the story now.

One of the highest-ranking transgender military officers in the world — if not the highest — is Lt. Col. Cate McGregor of the Australian Defense Force. When she decided to undergo gender reassignment in 2012, she offered to resign. But her boss, the chief of Army, Lt. Gen. David Morrison, refused to allow it. She is now a prominent and widely respected officer (and cricket commentator) who attributes her acceptance to her colleagues’ support and Australia’s “live and let live” pragmatism. Most “alpha Aussie blokes,” she says, were content that she was “still into chicks” and could still hit a cricket ball, which amused her: “There is a groping towards a paradigm of blokeyness they can accept.” Every day now, she says, living as a woman, “it feels amazing to be alive.”

General Morrison said that watching Colonel McGregor’s struggles has deepened his understanding of what it means to be transgender: “My hat goes off to everyone who does it because they are trying to be true to themselves. It takes an enormous amount of courage. And if an army can’t respect courage, then there’s something wrong.”

Courage, surely, should be part of any honor code, too.