The US military has reported a massive spike in sexual assaults, with 20,500 instances of unwanted sexual contact in 2018 - up from 14,900 in 2016 when a survey was last conducted, according to ABC News.

Most of the victims were female recruits aged 17 to 24, while alcohol was involved in approximately 1/3 of the incidents reported. Shockingly, just one out of three cases were reported to the authorities.

In response to the findings, Acting Defense Secretary Patrick Shanahan told Congress he plans to "criminalize" sexual harassment in the military.

The report released on Thursday surveyed the Army, Navy, Air Force and Marines, and found 20,500 cases in 2018. Incidents of unwanted sexual contact - which ranges from groping to rape - rose by around 38% between 2016 and 2018. Only one out of three cases were reported to authorities, the report found.

In over 85% of the cases, the victims knew their alleged attacker - and a disturbing number of incidents involved young women whose attacker was often their superior officer.

"We've got a higher prevalence for women 17 to 24. We're going to be focusing very, very tightly on that," said Nate Galbreath, Deputy Director of the Department' of Defense's Sexual Assault Prevention and Response Office.

"This is what tells us that there's something going on that we need to hone in on," he told ABC News.

"It's extremely disheartening," said Dr. Elizabeth Van Winkle, the executive director of the Office of Force Resiliency for the Defense Department. "These are our youngest service members and it is extremely frustrating because we've been working at this for a really long time."

New efforts will focus on lower-level leaders, starting with non-commissioned officers, and how they need to hold service members in their units accountable.

"Our command climate surveys for a long time measured toxic leadership," said Van Winkle. "What we're moving towards is that you're not only accountable for your own behavior but you're accountable for true command climate. You are accountable for what's happening within the peers underneath you."

"What we now have to do is we really have to focus down and work with the E5's (sergeants) and those first line folks that are right there on the front lines," said Galbreath. "To be able to say here are the tools that you can use to be able to set good order and discipline."