In addition to action against the IRA , the USC may have been involved in a number of attacks on Catholic civilians in reprisal for IRA actions , for example , in Belfast , the McMahon Murders of March 1922 , in which six Catholics were killed , and the Arnon Street killings a week later which killed another six . On 2 May 1922 , in revenge for the IRA killing of six policemen in counties Londonderry and Tyrone , Special Constables killed nine Catholic civilians in the area
Arnon Street killings
Arnon Street killings
Ulster Special Constabulary