bluejacket vs copilot

bluejacket

noun

  • A seaman of a British warship 

  • An enlisted man in the US Navy. 

  • A uniformed policeman. 

copilot

noun

  • A backup or assistant pilot of an aircraft. 

verb

  • To serve as relief or assistant pilot. 

How often have the words bluejacket and copilot occurred in a corpus of books? (source: Google Ngram Viewer )