bombproof vs redoubt

bombproof

noun
  • An air-raid shelter, a structure designed to give protection against air raids and bombs. 

adj
  • Sufficiently strong to resist the effects of a blast from a bomb. 

verb
  • To make resistant to bomb blasts. 

redoubt

noun
  • A place of safety or refuge. 

  • A reinforced refuge; a fort. 

  • A small, temporary, military fortification. 

  • The return of doubt. 

verb
  • To fortify, to make into a stronghold. 

  • To doubt again. 

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