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.