crewman vs water tender

crewman

noun
  • Synonym of armoured crewman 

  • A member of a crew, especially the crew of a ship. 

water tender

noun
  • A first-class petty officer in charge in a fireroom, who supplies the boilers with water, sees that fires are properly cleaned and stoked, etc. 

  • A specialized firefighting apparatus designed for transporting water from a water source, such as a lake or hydrant, to a fire scene. 

How often have the words crewman and water tender occurred in a corpus of books? (source: Google Ngram Viewer )