convoy vs passenger ship

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. 

passenger ship

noun
  • A ship whose primary function is to carry passengers. 

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