cadet vs lieutenant junior grade

cadet

noun
  • A student at a military school who is training to be an officer. 

  • Junior. (See also the heraldic term cadency.) 

  • A younger or youngest son, who would not inherit as a firstborn son would. 

  • A young gentleman learning sheep farming at a station; also, any young man attached to a sheep station. 

  • A participant in a cadetship. 

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. 

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