sapper vs zipperhead

sapper

noun
  • An officer or private of the Royal Engineers. 

  • Historical term for a combat engineer that is still used in some armies, in other words an engineer or a soldier engaged in attacking, destroying, and circumventing or building fortifications, bridges, and roads; a military engineer active in a combat zone. 

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 sapper and zipperhead occurred in a corpus of books? (source: Google Ngram Viewer )