An auxiliary force is a group affiliated with, but not part of, a military or police organization. In some cases, auxiliaries are armed forces operating in the same manner as regular soldiers. Most often, auxiliaries are civilian volunteer components supporting the main police or military force.

Historically the designation "auxiliary" has also been given to foreign or allied troops in the service of a nation at war.
The Auxiliary Division

Auxiliary Division

The Auxiliary Division of the Royal Irish Constabulary , generally known as the Auxiliaries or Auxies, was a paramilitary organization within the Royal Irish Constabulary during the Irish War of Independence....

 was a British paramilitary

Paramilitary

A paramilitary is a force whose function and organization are similar to those of a professional military, but which is not considered part of a state's formal armed forces....

 police force raised during the Irish War of Independence

Irish War of Independence

The Irish War of Independence , Anglo-Irish War, Black and Tan War, or Tan War was a guerrilla war mounted by the Irish Republican Army against the British government and its forces in Ireland. It began in January 1919, following the Irish Republic's declaration of independence. Both sides agreed...

 1919–21.