Sexual assault in the American military surged in the last two years, driven almost entirely by a 50 percent increase in assaults on women in uniform, according to a survey released on Thursday by the Defense Department.

The department’s annual Report on Sexual Assault in the Military estimated that there were 20,500 instances of “unwanted sexual contact” in the 2018 fiscal year, based on a survey of men and women across the Army, Navy, Air Force and Marines. That was an increase of 38 percent from the previous survey in 2016.

The grim data provide considerable ammunition for critics in Congress and veterans’ groups who have pressed repeatedly to change the way the military prosecutes sexual assault crimes. They want authority over such cases shifted away from military commanders and into the hands of an independent prosecutor’s office.

“These aren’t just numbers, these are people’s lives,” said Representative Jackie Speier, Democrat of California, who has pushed to remove the authority from commanders.