MARDET (short for "Marine Detachment") was a detachment of United States Marine Corps personnel who served aboard and provided security aboard large naval vessels serving in the United States Navy
In 1986, Commander Rogerson, the command duty officer aboard the aircraft carrier USS Enterprise (CVN-65), contacted the MARDET commanding officer to report that there was an intruder in the ship's #4 MMR. (Star Trek IV: The Voyage Home)