In the United States Navy, Refueling and Overhaul (ROH) refers to a lengthy process or procedure performed on nuclear-powered Naval ships, which involves replacement of expended nuclear fuel with new fuel and a general maintenance fix-up, renovation, and often modernization of the entire ship. particularly lengthy refueling, maintenance, and modernization process for a nuclear aircraft carrier can last up to almost three years and be referred to as a Refueling Complex Overhaul (RCOH) .