merchant marine vs watercraft

merchant marine

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

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

watercraft

noun
  • Any vessel with implements designed to move it in arbitrary direction through one or various bodies of water – a boat, ship, sea scooter, or similar vehicle. 

  • Skill in boating, swimming, or other water-related sports. 

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