Sir John Hermon , who died on Thursday aged 79 , was chief constable of the Royal Ulster Constabulary during the most fraught period in the force 's history , the years between 1980 and 1989 , when the RUC occupied the front line in the anti-terrorist campaign in Northern Ireland , the IRA took part in hunger strikes , the Republican movement began to politicise , controversial Orange marches were re-routed , and the Anglo-Irish agreement was signed .