Sub Lt Samuel Mitchell, 27, was cleared of two counts of rape following a four-day court martial trial.
The complainant said she told him "no sex" after a ball at Britannia Royal Naval College in Dartmouth.
The judge said it was "yet another case" where excessive alcohol consumed by service personnel had "led to disgraceful behaviour".
Click here for live updates on this story
Sub Lt Mitchell had been accused of the sexual attack on a fellow officer cadet after going into her room at the college following a Victory In Europe Day dinner on 8 May last year.
A panel of senior officers in Portsmouth cleared him of two counts of rape.
The complainant said she was too drunk and drowsy to articulate herself more clearly against having sex.
But the defendant told the trial that she made "pleasure noises" and told him he was "amazing" and told him he was "really good" at what he was doing.
She also admitted getting back into bed with the defendant after the sex and falling asleep next to him.
Judge Advocate General of the Armed Forces, Jeff Blackett, told Sub Lt Mitchell he took advantage of the woman.
"You should be absolutely clear that your behaviour on that evening was disgraceful and so was the way you conducted yourself afterwards," he said.
"It's not the conduct one expects of a naval officer, I hope you have learnt a lesson to respect your fellow officers of either sex."
A judge has criticised armed forces' drinking culture as a naval officer was cleared of raping a drunken colleague.