According to a new study, biologically male military service members are twice as likely to identify as transgender as civilians. The research also noted that transgender service members are more likely to volunteer for the more dangerous missions.

The report was written by George Brown, a preeminent expert on transsexuality in the military. In 1988, nearly 24 years ago, he wrote the first paper on the subject called "Transsexuals in the Military: Flight into Hypermasculinity." According to the 1988 paper, he said that enlistment in the military was "repudiation of feminine aspects of the self in a sexually dichotomized society can become a 'frantic preoccupation'."

The new paper, which has not yet been published, is an expansion of his original work. The case-study model has been replaced with a survey of 5 million service members.

The original paper was a case study of 11 individuals, three of whom who had not been in the military, and eight of whom were veterans, Department of Defense employees, or service members at the time. Brown himself expressed surprise at the notion: "Surely, a male who is gender dysphoric and engages in cross-gender activities and possibly sexual activity with other males would not voluntarily submit himself to a system known for its staunch intolerance of deviancy in any form, whether it be homosexuality, long hair, or wrinkled uniforms." But, he noted, all were requesting hormones or sexual reassignment surgery.

Bradley Manning, the soldier who handed over classified military information to WikiLeaks, and his defense team argued in court that his mental health had significantly deteriorated due to the military's treatment of transgender individuals.

Recently, transgender advocates made headlines as advocates have attempted to get the definition of gender identity disorder removed or rewritten in the American Psychiatric Association's upcoming fifth iteration of Diagnostic and Statistical Manual of Mental Disorders.

Brown's new research will be presented in San Francisco in the fall.