second lieutenant vs warrant officer

second lieutenant

noun
  • The lowest rank of a commissioned army officer, below a lieutenant. 

  • The lowest rank of a commissioned officer in the United States Army, United States Air Force, or United States Marine Corps, below a first lieutenant. The rank of second lieutenant is equivalent to the naval rank of ensign. 

warrant officer

noun
  • An officer holding rank by virtue of a warrant rather than a commission. 

  • An officer assigned to execute warrants and other writs. 

How often have the words second lieutenant and warrant officer occurred in a corpus of books? (source: Google Ngram Viewer )