troopship vs zipperhead

troopship

noun
  • A ship used to transport military troops. 

zipperhead

noun
  • A soldier in the Royal Canadian Armoured Corps or in the Armoured Crewman military trade. 

  • A person of East Asian descent. 

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