prepare to fire vs unload

prepare to fire

unload

verb
  • To reduce the vertical load factor on (an airplane's wing or other lifting surface), typically by pitching downwards toward the ground to decrease angle of attack and reduce the amount of lift generated. 

  • To remove (the load or cargo) from a vehicle, etc. 

  • To deposit one's load or cargo. 

  • To give vent to or express; to unburden oneself of. 

  • To discharge, pour, or expel. 

  • To get rid of or dispose of. 

  • To remove the load or cargo from (a vehicle, etc.). 

  • To remove the charge from. 

  • To deliver forcefully. 

  • To ejaculate, particularly within an orifice. 

  • To remove (something previously loaded) from memory. 

How often have the words prepare to fire and unload occurred in a corpus of books? (source: Google Ngram Viewer )