The report found only one in three cases was reported to the authorities (Picture: US Department of Defense).
The US military has reported a 13% rise in sexual assaults last year, with an anonymous survey of service members suggesting the problem is much larger.
More than 20,000 service members said they had experienced some type of sexual assault, but only a third of those had filed a formal report, according to results released on Thursday.
That is up from around 15,000 in 2016, the last time a survey was conducted.
The figure is based on reports of attacks as well as survey data, which was gathered through a poll of over 100,000 US troops.
Alcohol was involved in one-third of cases, and young female recruits aged 17 to 24 were at the highest risk of attack.
The report found only one in three cases was reported to the authorities.
Senator Kirsten Gillibrand, a New York Democrat, said: "I am tired of the statement I get over and over from the chain of command: 'We got this, madam, we got this'. You don't have it!
"You're failing us."
The US Marine Corp had the largest jump last year, at 23%, the Army more than 18%, while the US Navy saw a 7% increase and the US Air Force was up by about 4%.
In the vast majority of cases, the alleged perpetrator was a military man, often near the same rank as the victim and usually someone they knew.
The increase in assaults has triggered another round of new Pentagon programmes and initiatives to try to reduce misconduct.