In response to ongoing violence and rebellion in Ireland and a brutal campaign of attrition against members of the RIC (Royal Irish Constabulary), the ADRIC was recruited in Great Britain from among ex-officers who had served in World War I, especially those who had served in the British Army (including the Royal Flying Corps). Most recruits were from Britain, although some were from Ireland, and others came from other parts of the British Empire. Recruiting began in July 1920, and by November 1921, the division was 1,900 strong. The Auxiliaries were nominally part of the RIC, but actually operated more or less independently in rural areas.

The Auxiliaries were a group of undisciplined mercenaries who wreaked havoc in Ireland 1920-21. While the Black and Tans are reviled in Irish history as murderous thugs, their role was primarily as a back-up unit to what often amounted to search and destroy operations conducted by the Auxiliaries.

The Auxiliaries most infamous action occurred on Bloody Sunday, 21 November 1920. Following the assassination of twelve British intelligence operatives (the Cairo Gang) on the orders of Michael Collins, Auxiliary troops forced their way into Croke Park, Dublin where up to 5,000 people were watching a football game between Tipperary and Dublin. The troops fired indiscriminately into the crowd killing fourteen people. On 11th December, Auxiliaries rampaged through Cork City, burning parts of the city to the ground in retaliation for an ambush they suffered earlier in the day.

Photo: A group of Auxiliaries and “Black and Tans” in Dublin, April 1921