The number of sex-related crimes occurring in U.S. military communities is far greater than the Defense Department has publicly reported, a U.S. senator said Monday in a scathing critique that asserts the Pentagon has refused to provide her information about sexual assaults at several major bases.

The spouses of service members and civilian women who live or work near military facilities are especially vulnerable to being sexually assaulted, Sen. Kirsten Gillibrand, D-N.Y., said in a report. Yet they "remain in the shadows" because neither is counted in surveys conducted by the Defense Department to determine the prevalence of sexual assaults within the ranks, the report said.

“I don't think the military is being honest about the problem,” Gillibrand said in an interview.

The senator said her analysis of 107 sexual assault cases found punishments that were too lenient and the word of the alleged assailant was more likely to be believed than the victim.

Less than a quarter of the cases went to trial and just 11 resulted in conviction for a sex crime. Female civilians were the victims in more than half the cases, according to Gillibrand, an outspoken advocate for an overhaul of the military justice system.

In its annual report on sexual assaults in the military released Friday, the Defense Department reported progress in staunching the epidemic of sexual assaults. It estimated that sex crimes are decreasing and more victims are choosing to report them — a sign that there is more confidence that offenders will be held accountable.

Laura Seal, a Defense Department spokeswoman, said the department does not have authority to include civilians in its surveys.

In one of the cases Gillibrand reviewed, an airman allegedly pinned his ex-girlfriend down and then raped her. During the investigation, two other civilian victims stepped forward to accuse the same airman of sexual assault.

One of them, the wife of another service member, awoke in the night to find the airman in bed with her. Two of his fingers were inside her vagina. The investigating officer recommended the airman be court-martialed. If convicted, he faced a lengthy prison term.

But the investigator's superiors decided against a trial. They used administrative procedures to discharge the airman under “other than honorable conditions.” The Air Force said the victims preferred this course of action. Two of them had decided they “wanted no part in the case,” according to the Air Force, while the third said he did not want to testify.

To Gillibrand, the outcome was suspicious and suggested the victims may have been intimidated.

“It's frustrating because you look at the facts in these cases and you see witnesses willing to come forward, getting the medical exam and either eventually withdrawing their case or the investigators deciding that her testimony wasn't valid or believable,” she said.

The report said the case files contradict the Pentagon's assertion that military commanders will be tough on service members accused of sex crimes. Gillibrand has backed legislation that would remove commanders from the process of deciding whether serious crimes, including sexual misconduct cases, go to trial. That judgment would rest with seasoned military attorneys who have prosecutorial experience. The Pentagon is opposed to the change.

Gillibrand's request for the case files followed a February 2014 investigation by The Associated Press into the U.S. military's handling of sexual assault cases in Japan that revealed a pattern of random and inconsistent judgments in which most offenders are not incarcerated. AP obtained through the Freedom of Information Act more than 1,000 reports of sex crimes involving U.S. military personnel based in Japan between 2005 and early 2013.

To determine whether the same situation existed at major U.S. bases, Gillibrand asked then-Defense Secretary Chuck Hagel for the details of sexual assault cases investigated and adjudicated from 2009 to 2014 at four large U.S. military bases: the Army's Fort Hood in Texas, Naval Station Norfolk in Virginia, the Marine Corps' Camp Pendleton in California and Wright-Patterson Air Force Base in Ohio.

In December, nearly 10 months later, the Pentagon provided case files just for 2013, Gillibrand said, and those 107 cases were delivered only after former Sen. Carl Levin, then chairman of the Senate Armed Services Committee, intervened. At the time, Gillibrand led the committee's military personnel panel.

The refusal to provide the data, Gillibrand's report said, “calls into question the department's commitment to transparency and getting to the root of the problem.”

Seal said the scope of Gillibrand's request was “extraordinary.” The senator and the department “came to an agreement to provide a subset of the documents originally requested.”

Gillibrand said she still wants the files from the other years.

The senator also questioned whether the 107 cases represented the actual total for the four bases. There were five for Wright-Patterson even though the base told AP its legal office had received nine allegations of sexual assault in 2013. There were 15 cases for 2013 at Naval Station Norfolk, the largest naval installation in the world with 43,000 service members stationed there.

In another case cited by Gillibrand, a married, 34-year-old Marine Corps staff sergeant received a reduction in rank and was docked $2,042 in pay after forcing a 17-year-old girl to have sex with him.

They met on an online dating website called Plenty of Fish. She said she was 18 and he said he was 24. After a date, she returned with him to his room and had a glass of wine. He got on top of her and kept asking if she "wanted it," according to the records. She repeatedly told him to stop and get off of her. He ignored her.

The Air Force investigating officer said the victim was not a credible witness because there were glaring inconsistencies in her story. Under the terms of a pretrial agreement, a sexual assault charge was withdrawn. The Marine pleaded guilty to providing alcohol to a minor, making a false statement and adultery.

The Associated Press