Command duty officer
A command duty officer (CDO, on a naval ship) or officer of the watch (OOW, on a merchant ship) is the head duty officer (officer of the day) on a ship, entrusted by the commanding officer and executive officer (on a naval ship) or the shipmaster (on a merchant ship) with exercising in their absence command and control of the ship on their behalf for the duration of a watch. == Navy == In the US Navy, the Command Duty Officer carries out the duties of the commanding officer "in the absence of the commanding officer or the executive officer, or both." The CDO supervises other junior watchkeeping officers such as the officer of the deck.