flotilla vs merchant marine

flotilla

noun
  • A small fleet of warships (usually of the same class), or a fleet of small ships. 

merchant marine

noun
  • Synonym of merchant navy. The fleet considered as an entire combined force. 

  • A ship dedicated to commercial, rather than military, purposes. 

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