In 1970 – 71 , Catholics made up about 36 % of the population and about 18 % of the UDR . By the end of 1972 the number of Catholics in the UDR had dropped to 3 % and never rose above that figure again . There are a number of reasons for this . In the early years of the conflict , relations soured between the Catholic community and the Army . This was mainly due to incidents such as the Falls Curfew , internment , Bloody Sunday and Operation Motorman . There were also frequent claims of UDR soldiers abusing Catholics at checkpoints and during house searches . Catholic Church and Irish nationalist leaders withdrew their support for the regiment . Many Catholic soldiers left the regiment due to pressure and intimidation from their own community , and the IRA 's policy of singling out Catholic soldiers for assassination . Catholics within the regiment also reported being intimidated by Protestant fellow soldiers . Other Catholics resigned in protest at what they saw as the Army 's harsh and biased treatment of their community , especially after Operation Demetrius ( the introduction of internment ) . The '' Belfast Telegraph '' reported that 25 % of the regiment 's Catholics resigned in 1971 , half of those in the months following Operation Demetrius . By the end of 1972 , the vast majority had resigned or simply stopped turning up for duty
Bloody Sunday
Bloody Sunday (1972)
Ulster Defence Regiment