ambulance vs casualty department

ambulance

noun
  • A mobile field hospital. 

  • An emergency vehicle designed for transporting seriously ill or injured people to a hospital. 

verb
  • To transport by ambulance. 

casualty department

noun
  • (also casualty ward) the department of a hospital providing immediate treatment for emergency cases. Called emergency room in North America. 

How often have the words ambulance and casualty department occurred in a corpus of books? (source: Google Ngram Viewer )