Citizens volunteered to enroll in the Home Defense League to aid police in patrolling duties and be on hand in case of emergencies.

If the need arose (as it did in 1917 when armed forces were mobilized), they could be called into service to guard armories, subway stations, and other areas of the city.

[5] In 1918, the Home Defense League changed its name to the New York Reserve Police Force, as proposed by Commissioner Richard Enright, in addition to undergoing higher-caliber training under Special Deputy Police Commissioner Lewis Rodman Wanamaker.

[7][8] Governor Alfred E. Smith signed a new state law in 1920 that established the permanency of a reserve force as an adjunct of the police department.

By war's end in 1945, the corps was disbanded, but the city continued to maintain a volunteer police unit.

In 1951, the New York State Legislature enacted the "Defense Emergency Act" requiring New York City to recruit, train, and equip volunteer Civil Defense wardens, who would provide traffic and crowd control and other assistance to police officers in the event of an emergency or natural disaster.

The New York Penal Law provided peace officer status for the Civil Defense wardens during the event of an actual natural or man-made disaster or attack or during training drills.

On March 20, 2020, the NYPD suspended the Auxiliary Police unit due to concerns regarding the COVID-19 pandemic.

All Auxiliary Police officers are required by New York State to pass an annual refresher course in the use of force with the straight baton, arrest procedures, and law in order to maintain their status.

The word "AUXILIARY" is placed on the trunk, hood, and front and rear side panels of the vehicles with a red underline.

Auxiliary Police Officers are equipped with straight wood batons when assigned to normal patrol, ASP batons (when assigned to bicycle patrol), bullet resistant vests, police radios directly linked to the Central Dispatcher, flashlights; whistles, handcuffs, notebooks, and reflective traffic vests.

Transit Auxiliary Police periodically perform inspections of the subway station(s) and platforms which they are assigned to, taking note of any suspicious occurrences, and set up a fixed post at the subway turnstiles, token booths, mezzanines, or platforms.

All applicants to this unit are required to have a minimum of five years experience as a patrol officer with the NYPD Auxiliary Police, must be mature, and have exceptional discipline and service records.

[20] Auxiliary Response Team: Established in 2024, officers in this unit are tasked with responding to rapid deployments such as creating presence in areas seeing a rise in crime.

[21] Undercover Vice Ops: Officers that have not reached the age of 21 years old (18-20 1/2) can be utilized to assist the NYPD Vice Unit Narcotics Division for "Quality of Life enforcement" stings which address illegal alcohol, knife, and spray paint sales.

[22] [DEFORMED] Patrol Support Unit: Also known as Auxiliary Resuce, officers would respond to incidents such as vehicle accidents and entrapments.

The vehicle used was either a 1990s older model GMC Stepvan or Ford F350 Van, similar to the ESU REP truck.

Once the vehicle attains a certain amount of mileage, it is taken out of service and is either redecaled and given to a command for the Auxiliary Police, or is sold.

On March 14, 2007, two Auxiliary Police officers—Eugene Marshalik and Nicholas Pekearo—were killed in a shootout in Greenwich Village.

But after the shootings of Pekearo and Marshalik, Mayor Michael R. Bloomberg and Commissioner Raymond W. Kelly asked the New York City Council to earmark more than $3.3 million to provide all Auxiliary Police officers with Level IIIA Vests, the same used by full-time officers.

On March 27, 2007, the City Council approved this bill, which had all Auxiliary officers equipped with vests.

Since then, in 2010, funding for vest for Auxiliary Police Officers has run out of the NYPD City Budget.

Although part-time volunteers, NYC APOs face many issues similar to those faced by paid employees, including health and safety conditions and NYPD disciplinary procedures, and the need for their interests to be represented to city, state and federal government, and other entities beyond the NYPD.