The New York City Police Department (NYPD), started in 1844, is the largest police force in the United States. It is the police force that serves the five boroughs of New York City. The NYPD was one of the first "modern" style police departments in the United States with the Boston Police Department. The NYPD uses a color of the day to allow uniformed officers to recognize undercover officers to prevent accidental shootings. 