Command duty officer
A command duty officer (CDO) or officer of the day (OOD) is a watchkeeping officer on a naval ship who is delegated authority from a commanding officer of the ship and holds command and control of the ship during that watch. A CDO represents the commanding officer and executive officer in their absence, and supervises other junior watchkeeping officers such as the officer of the deck. Command duty officers are typically assigned for ships in port or land naval installations. While many watchkeepers stand watch for a few hours continuously at a time, CDOs may be on duty for longer periods, such as a day or a week. Whilst the CDO may be outranked by more senior officers on board, the CDO is only subordinate to the commanding officer and executive officer whilst carrying out their duties.

In the Royal Navy, and other navies based upon this structure, the position is known as an officer of the day, and other duties may include ceremonial duties (such as carrying out Colours or Sunset) and taking charge in emergency situations in the damage control headquarters.  Generally on warships, the OOD will be a commissioned junior officer who holds a harbour watchkeeping certificate.  On shore establishments, a warrant officer may be used to augment the duty roster.

In the United States Navy, CDOs may also be found on larger warships while underway.

See also 

 Duty officer

References 

Naval ranks
Command and control