Four members of the U.S. Navy have been accused of engaging in a sex with an underage girl on a naval base and recording and photographing the illicit encounter, according to charge sheets released to NBC News.

Three of the sailors are accused of engaging "group sex" with the girl, who was between 12 and 16 years old, while a fourth is accused of penetrating the girl with his finger and groping her. Two of the defendants are also accused of producing child pornography.

The alleged sex acts took place in September 2017 at Naval Base Kitsap-Bangor in Washington, the main submarine base in the Pacific Northwest. It's not known how the girl got into the barracks.

An Article 32 hearing, which is similar to a civilian preliminary hearing and determines if the sailors, who were not named, should go to court-martial, was held on Sept. 24. It typically takes 10 days for the hearing officer to make a recommendation on the charges to the sub's commanding officer, according to Navy Times, which first reported the charges.

"Following the Convening Authority's decision, the accused will be arraigned on the charges that were referred to court-martial. As with any court proceeding, the accused are presumed innocent until proven guilty at court-martial," Cmdr. Michael Smith, the public affairs officer for Submarine Group Nine, wrote to NBC News in an email.

Smith confirmed the four sailors are still on active duty, with two sailors assigned to the USS Nebraska, one assigned to the USS Henry M. Jackson, and the fourth who was assigned to the USS Henry M. Jackson but has since been reassigned to the Naval Submarine Support Center in Bangor, Washington.

"The U.S. Navy holds its personnel to the highest standards of conduct. We are committed to holding our personnel accountable for their actions and preserving good order and discipline throughout the fleet," Smith said.