WASHINGTON – Child sex offenders are the largest category of inmates in U.S. military prisons, yet a full accounting of their crimes and how much time they’re actually locked up for is shielded by an opaque system of justice, an Associated Press investigation has found.

Of the 1,233 inmates confined in the military’s prison network, 61 percent were convicted of sex crimes, according to the latest available data, obtained through the federal open records law. Children were the victims in over half of those cases.

Since the beginning of this year alone, service members victimized children in 133 out of 301 sex crime convictions, with charges ranging from rape to distributing child pornography.

Child sex assaults in the military have received scant attention in Washington, where Congress and the Defense Department have focused largely on preventing and prosecuting adult-on-adult sex crimes.

Daniel E. DeSmit, a Marine Corps chief warrant officer, spent at least $36,000 viewing and producing child pornography over the span of six years. In emails examined by Navy criminal investigators, DeSmit described his preference for sex with prepubescent girls as “the best experience.”