First officer

First officer may refer to:

• Chief mate, the second-in-command (usually) of a merchant ship
• First officer (civil aviation), the second pilot of a civil aircraft
• Executive officer (military), the second-in-command of a naval vessel
• The most senior civil service position in the United States Foreign Service, with responsibility for running an embassy under the authority of and reporting to the ambassador
• Air Transport Auxiliary rank corresponding to Flight Lieutenant in the Royal Air Force
• Women's Royal Naval Service rank corresponding to Lieutenant-Commander in the Royal Navy