fire engine vs fire truck

fire engine

noun
  • A vehicle used by firefighters to pump water to fight a fire. Typically, a fire engine carries a supply of water and has the ability to connect to an external water supply. 

fire truck

noun
  • A ladder truck, a vehicle used by firefighters to gain access to the upper stories of a building. Typically, a fire truck has a hydraulic system which operates a large, heavy-duty ladder mounted on top of the truck body, space for portable ladders to be stored and compartments for holding other tools that may be needed. Unlike a fire engine, trucks do not have pumps or carry water. 

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