air force vs artillery

air force

noun
  • A branch of the military mainly devoted to air warfare, as opposed to (land) army and navy. 

  • A unit in the U.S. Air Force larger than a division but smaller than a command. 

artillery

noun
  • An army unit that uses such weapons, or a military formation using projectile weapons, such as archers. 

  • Large projectile weapons, in modern usage usually large guns, but also rocket artillery. 

  • Gunnery. 

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