helper vs lieutenant junior grade

helper

noun
  • One who helps; an aide; assistant; auxiliary. 

  • That which helps; anything serving to assist. 

  • A locomotive that assists a train, usually on steep gradients. 

  • A person who does cleaning and cooking in a family home, or in a market; domestic employee. 

lieutenant junior grade

noun
  • 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. 

  • 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. 

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