lieutenant junior grade vs underling

lieutenant junior grade

noun
  • A commissioned officer of the United States Navy whose rank is above an ensign's and below a lieutenant, or a corresponding rank in other navies. 

  • A commissioned officer in the United States Coast Guard, Public Health Service, or National Atmospheric and Oceanic Administration whose rank is above an ensign and below a lieutenant. 

underling

noun
  • A subordinate, or person of lesser rank or authority. 

  • A low, wretched person. 

How often have the words lieutenant junior grade and underling occurred in a corpus of books? (source: Google Ngram Viewer )