Chichester-Clark won the leadership election to replace O'Neill and swiftly moved to implement many of O'Neill 's reforms . Civil disorder continued to mount , culminating in August 1969 when Catholic Bogside residents clashed with the Royal Ulster Constabulary in Derry because of an Apprentice Boys of Derry march , sparking days of riots . Early in 1971 , Chichester-Clark flew to London to request further military aid following the 1971 Scottish soldiers ' killings . When this was all but refused , he resigned to be replaced by Brian Faulkner
1971 Scottish soldiers ' killings
1971 Scottish soldiers' killings
Ulster Unionist Party