GROTON, Conn. (AP) — Sailors involved in the secret video recording of female officers in the dressing area of a U.S. Navy submarine will face "significant penalties," the admiral in charge of the submarine force said Thursday.

A dozen sailors are under investigation in the scandal aboard the USS Wyoming, one of the first American submarines to have female officers.

"What some people thought was a high-schoolish prank was a serious sexual offense, with significant penalties," Vice Adm. Michael Connor said.

The recording and distribution of the videos are a setback for the high-profile introduction of mixed-gender crews on submarines, which had been one of the last areas of the armed forces closed to women before the Navy reversed a ban in 2010. More than 50 women are serving aboard submarines, a female officer in Connecticut became the first woman assigned to a Los Angeles-class attack sub last week, and the Navy is expected soon to introduce enlisted female submariners as well as officers.

The recording took place in a changing area that is used by male and female officers aboard the Wyoming, a nuclear-armed submarine based at Kings Bay Naval Submarine Base in Georgia. Typically, female officers put up a sign to indicate when the shower area is in use by women.

Connor, who was visiting Connecticut for a change of command ceremony aboard a Groton-based submarine, said in an interview with The Associated Press that the biggest concern is that the recordings did not come to authorities' attention until recent months, even though they had been taken a year ago and shared among a number of sailors. He said it happened despite the Navy's best efforts to prepare the submarine-force culture for coed crews.

"Out of a force of 17,000 people we have a very small number of folks who didn't get it, and they're going to learn," Connor said during a talk earlier in the day at a veterans' hall in Groton.

Twelve sailors are being investigated for the creation and distribution of the recordings, according to Lt. Cmdr. Tommy Crosby, a Navy spokesman. He said the investigation by the Naval Criminal Investigative Service has been completed and military lawyers are reviewing how to proceed with prosecution.

Connor said the actions of a few sailors should not take away from the successful integration of women. He said more than 100 women are in the submarine program, including those in training, and some female officers will soon be teaching at the Navy's submarine school in Groton.

The integration of women began in 2011 on ballistic-missile subs, which were seen as more capable of accommodating mixed-gender crews because they have more room than the cramped attack submarines. USS Minnesota, which is based at Naval Submarine Base New London in Groton, last week became the first attack sub of its class to receive a female officer, Crosby said.

The Wyoming case also highlights the difficulty faced by the Navy as it tries to develop a policy for iPhones and other electronic devices that can pose security risks but are also seen as boosting morale.

"We thought and we continue to think we had struck the proper balance between having them on the ship," Connor said. "Obviously, they were misused in this case."