"Sexual assault is a crime and a contradiction to everything we stand for," he said.
The NCIS provided more than 600 case files — seven years of detailed but heavily redacted executive summaries of sex-crime reports. The four military branches provided another 400 files covering narrower time frames.
The Pentagon has said its commanders have been using nonjudicial punishment less frequently in recent years. But the documents show that in Japan at least, U.S. commanders are using that authority more often. This is especially true in the Navy, where in 2012 only one case led to court-martial. In the 13 others, commanders used nonjudicial penalties rather than ordering trials.
The authority to decide how to prosecute serious criminal allegations would be taken away from senior officers under a bill crafted by Gillibrand and expected to come before the Senate as early as this coming week. The legislation would place that judgment with trial counsels who have prosecutorial experience and hold the rank of colonel or above.
Senior U.S. military leaders oppose the plan, saying it would undermine the ability of commanders to ensure discipline within their ranks.
"Taking the commander out of the loop never solved any problem," said U.S. Sen. Lindsey Graham of South Carolina, a former Air Force lawyer who is the personnel subcommittee's top Republican. "It would dismantle the military justice system beyond sexual assaults. It would take commanders off the hook for their responsibility to fix this problem."
Graham, a member of the Air Force Reserves who is an instructor at the service's judge advocate general school, said victims of sexual assault have a far better chance of getting justice than do victims whose cases are handled by civilian courts.
But research by Cassia Spohn, a professor of criminology and criminal justice at Arizona State University, found that civilian courts prosecute sexual assault cases at a higher rate than the military — 50 percent compared with 37 percent.