The AP story "shows the direct evidence of the stories we hear every day," said Gillibrand, who leads a group of lawmakers from both political parties pressing for further changes in the military's legal system.
"The men and women of our military deserve better," said Gillibrand, D-N.Y. "They deserve to have unbiased, trained military prosecutors reviewing their cases, and making decisions based solely on the merits of the evidence in a transparent way."
Air Force Col. Alan Metzler said the Department of Defense has been open in acknowledging that it has a problem.
"We have owned that," he said. "We have been public about it."
Metzler, deputy director of the Defense Department's Sexual Assault Prevention and Response Office, said the changes in military law and policy made by Congress and the Pentagon are creating a culture where victims trust that their allegations will be taken seriously and perpetrators will be punished. The cases in Japan preceded reforms the Pentagon implemented in May, according to defense officials.
The military, Metzler noted, is making progress. The number of sexual assault cases taken to courts-martial military-wide has grown steadily, from 42 percent in 2009 to 68 percent in 2012, according to department figures. In 2012, of the 238 service members convicted, 74 percent served time.
That trend is not reflected in the Japan cases. Out of 473 sexual assault allegations against sailors and Marines between 2005 and 2013, just 116, or 24 percent, ended up in courts-martial.
Further, the 238 convictions are a small number compared with the estimated 26,000 sex crimes that may have occurred that year across the military, according to the department's anonymous survey of military personnel. Sex crimes are vastly underreported in both military and civilian life.
The top U.S. officer in Japan, Lt. Gen. Salvatore Angelella, said the military takes the issue of sexual assault "very seriously."