chief mate vs first officer

chief mate

noun
  • In the merchant navy, the officer who is second in command to the captain, and whose primary duties include managing the maintenance and upkeep of the vessel. 

first officer

noun
  • The executive officer, second in command of a naval vessel. 

  • 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. 

  • The copilot of an aircraft. 

  • The chief mate of a merchant ship. 

  • The most senior civil servant in the United States Foreign Service, with responsibility for running an embassy under the authority of and reporting to the ambassador. 

How often have the words chief mate and first officer occurred in a corpus of books? (source: Google Ngram Viewer )