field gun vs howitzer

field gun

noun
  • An artillery piece, originally a smaller gun that could accompany a field army on the march and when in combat could be moved about the battlefield in response to changing circumstances. 

howitzer

noun
  • A cannon that combines certain characteristics of field guns and mortars, delivering projectiles with medium velocities, usually with relatively high trajectories; normally a cannon with a tube length of 20 to 30 calibers. 

  • A powerfully hit shot. 

verb
  • To attack with a howitzer. 

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