At the Pentagon, officials are grappling with a resurgence of cases in which troops trained to prevent sexual assault or harassment are being accused of committing it. (Charles Dharapak/Associated Press)

The Army is grappling with a resurgence of cases in which troops responsible for preventing sexual assault have been accused of rape and related crimes, undercutting the Pentagon’s claims that it is making progress against sexual violence in the ranks.

In the most recent case,an Army prosecutor in charge of sexual assault investigations in the Southwest was charged by the military last month with putting a knife to the throat of a lawyer he had been dating and raping her on two occasions, according to documents obtained by The Washington Post.

Additionally, a sergeant at Fort Sill, Okla., who was certified as a sexual assault prevention officer was convicted at a court-martial in May of five counts of raping a preteen girl.

Army officials confirmed to The Post that eight other soldiers and civilians trained to deter sex offenses or help victims have been investigated over the past year in connection with sexual assault. The Army would not provide details, saying that many of the investigations are pending.

Other branches of the armed forces have faced their own embarrassments. The deputy director of the Air Force’s office of sexual assault prevention at the Pentagon resigned last year after the Air Force inspector general rebuked him for making sexually inappropriate comments and creating “an intimidating and offensive working environment,” according to a confidential report obtained by The Post under the Freedom of Information Act.

Air Force staff members complained that the senior executive, Jay Aanrud, made sexist remarks about tight pants and Hooters models, and said it is women’s work to shop and eat bonbons, according to the report. Aanrud, a former pilot whose call sign was “Hoser,” told investigators that he was joking and that his remarks were misconstrued.

Despite the investigation, the Air Force rehired Aanrud last month to work at the Pentagon as a technical specialist on aviation issues. An Air Force spokeswoman said he doesn’t supervise anyone in his new job. Aanrud ­declined to comment.

For the armed forces, the cases are a painful reminder of similar scandals in 2013.

That year, the Air Force’s chief sexual assault prevention officer at the Pentagon was accused of groping a woman outside a bar; he was later acquitted by a civilian jury but reprimanded by the military. An Army sergeant in charge of helping sexual assault victims at Fort Hood, Tex., was convicted of pandering for pimping female soldiers.

In addition, each of the military services was tainted by ­reports of young women being assaulted by uniformed recruiters.

With angry lawmakers in Congress demanding a crackdown, then-Defense Secretary Chuck Hagel ordered the armed forces in May 2013 to retrain and rescreen tens of thousands of military ­recruiters and sexual assault prevention officers.

Despite the measures, incidents kept happening. Five months after Hagel’s order, a soldier attending a sexual assault prevention conference in Orlando was accused of getting drunk and raping a woman he met at his hotel. The Army investigated but did not file charges because the woman declined to cooperate.

Since then, the military has invested millions of additional dollars in sexual assault awareness programs. Training is mandatory for everyone in uniform. Top brass have promised to redouble their efforts to punish offenders and protect victims.

“We’ve been putting extraordinary resources into this area,” said Rep. Mike Coffman (R-Colo.), chairman of the House Armed Services subcommittee for military personnel. “Of all the issues we have on my committee, we have spent more time on sexual assault than any other issue.”

Coffman said military leaders have come a long way in addressing the problem but added that more needs to be done. He said Army leaders have briefed him about the sexual assault prevention officers who have been accused of sexual assault and said they are reviewing how people are selected for those posts.

“We always need to look at the screening and look where the screening failed,” Coffman said in an interview. But in comparison with past scandals, he said, “the Army has gotten the message an awful lot quicker.”

Last year, the Defense Department received 6,172 reports of sexual assault in the ranks — a new high and almost twice as many as were reported in 2010. Pentagon officials have called the increase a sign that more victims are willing to come forward and trust the military to help them.

To tackle the problem, the Army employs 650 full-time sexual assault response coordinators and victim advocates, plus 2,200 others who work part time.

In the past year, eight of them have been accused of sexual ­assault, triggering criminal investigations by a combination of military and civilian authorities, said William J. Sharp, an Army spokesman at the Pentagon.

Officials from the Navy, the Marines and the Air Force told The Post that none of their personnel involved in sexual assault prevention have been investigated for sex crimes over the past year.

Lt. Col. Jennifer R. Johnson, an Army spokeswoman, said the service adopted new standards in 2013 for screening sexual assault prevention personnel, drill instructors, recruiters and others who hold positions of “significant trust.”

She said that the standards are more stringent than the Defense Department requires, but that the Army has decided to review them again “to determine if any changes are required.”

“As Army professionals, we expect everyone on our team to live and demonstrate the Army values every day,” Johnson said in an email. “Every allegation of sexual assault, from an unwanted touch over the clothing to a forcible rape, is investigated. . . . The Army strives to hold all offenders accountable for their actions no matter their position or rank.”

Few personnel get more screening than the Army’s special-victim prosecutors, a team of 23 lawyers who oversee sex crime and domestic violence cases across the country. The job is considered an elite position within the Judge Advocate General’s Corps, and those who hold it are handpicked by the Army’s top uniformed lawyer.

The program was thrown into turmoil in 2014 when its supervisor was placed under investigation for allegedly groping a female lawyer — at a sexual assault prevention conference.

The supervisor, Lt. Col. Jay Morse, acknowledged having an intimate encounter with the woman but denied touching her without consent. Army officials ultimately decided that they lacked evidence to press criminal charges, but Morse was reprimanded for misconduct. He retired soon after.

The Army has since been rattled by another case involving a special-victim prosecutor.

In August 2016, a lawyer who worked for the Army walked into the Comanche County Courthouse in Lawton, Okla., to seek a protective order against a man she had been dating: Capt. Scott Hockenberry, who handled cases at Fort Sill and other posts in the region.

The woman alleged in court papers that their relationship had turned violent and that Hockenberry had raped her three times over the previous month. She also alleged that he had placed a knife against her throat during one of the assaults and injured her jaw on another occasion, according to her protective-order application.

“They started dating, but it got out of control,” said Robert Don Gifford, an attorney for the woman.

Hockenberry disputed the allegations and has filed a defamation claim against the woman in state court in Oklahoma, documents show.

The Army reassigned him to the Military District of Washington and conducted a lengthy criminal investigation.

Last month, it charged Hockenberry with sexually assaulting the woman on two occasions, placing a knife against her throat and striking her in the face, according to military charging documents obtained by The Post. A preliminary hearing is scheduled later this month.

“We categorically deny all of the allegations made by this accuser. Period. Full stop,” said Will Helixon, an attorney representing Hockenberry.

The Post’s policy is not to identify victims of sexual assault or abuse in most cases.

It is unclear why the Army waited a year to file charges. Lawyers for both sides say the case has attracted notice at the Pentagon, given the nature of Hockenberry’s job. “This has received extra scrutiny,” Gifford said.

Another recent case that has received high-level attention surfaced in August at Fort Benning, Ga., a boot-camp hub for the Army.

The Army suspended several drill instructors after female recruits reported being sexually assaulted. A criminal investigation is pending. The Army has released few details, although it has since relieved a Fort Benning battalion commander because of “a loss of confidence in his ability” to lead.