centurion vs senior captain

centurion

noun
  • An officer of the ancient Roman army, in command of a century of soldiers. 

  • A player who scores a century. 

  • A pilot in the United States Navy who has performed 100 night landings on an aircraft carrier. 

senior captain

noun
  • a military rank for a field officer above that of captain and below that of major 

  • a military rank for a naval officer above that of captain and below the admiral ranks or flag ranks 

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