convoy vs merchant marine

convoy

noun
  • One or more merchant ships sailing in company to the same general destination under the protection of naval vessels. 

  • The act of convoying; protection. 

  • A group of vehicles travelling together for safety, especially one with an escort. 

verb
  • To travel under convoy. 

  • To escort a group of vehicles, and provide protection. 

merchant marine

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

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

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