digger vs doughboy

digger

noun
  • A tool for digging. 

  • A spade (playing card). 

  • An Australian soldier. 

  • A large piece of machinery that digs holes or trenches. 

  • One who digs. 

doughboy

noun
  • An American infantryman, especially one from World War I. 

  • A kind of flour dumpling. 

  • Frybread. 

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