Support for the IRA increased further after Bloody Sunday in January 1972 , when thirteen unarmed men and boys were shot dead by the British Army 's Parachute Regiment at a march in the Bogside ( a 14th man was wounded and died 4 ½ months later ) . The support began to wane after the killing by the Official IRA of a local youth who was home on leave from the British Army . After a Provisional IRA ceasefire , during which it entered talks with the British government , broke down , the British took the decision to move against the " no @-@ go " areas . Free Derry came to an end on 31 July 1972 , when thousands of British troops moved in with armoured cars and bulldozers to occupy the area .