Belfast's Bloody Sunday

July 10, 1921:

On 8 July, the RIC attempted to enter the mainly Catholic and republican area around Union Street and Stanhope Street. However, they were confronted by about 15 IRA volunteers in a firefight that lasted over three hours.
The following day, 9 July, the IRA ambushed an armoured police truck on Raglan Street, killing one RIC man, injuring two more and destroying their armoured car. Around 14 IRA men took part in the operation. They had been alerted to the police presence by local residents banging dustbin lids to warn the IRA of the RIC patrol.
This sparked an outbreak of ferocious fighting between Catholics and Protestants in west Belfast on the following day, Sunday 10 July, in which 16 civilians (11 Catholics and 5 Protestants) lost their lives and 161 houses were destroyed. Of the houses destroyed, 150 were Catholic.
Gun battles raged all day along the sectarian 'boundary' between the Falls and Shankill Roads and rival gunmen used rifles, machine guns and hand grenades in the clashes. Gunmen were seen firing from windows, rooftops and street corners. A "Loyalist mob, several thousand strong" attempted to storm the Catholic Falls Road, carrying petrol and other flammable materials.
Another four people died over the following two days. While the IRA was involved in the violence, it did not control the actions of the Catholic community. An IRA officer reported that "the Catholic mob is almost beyond control".
The violence occurred only one day before a truce between the IRA and British forces formally ended the conflict - though in the north the official truce did not end the fighting. IRA members later recalled, "The Truce was not observed by either side in the north". The leader of the Belfast IRA's Active Service Unit, Roger McCorley, stated that "the Truce lasted six hours only".

I wasn't familiar with this Bloody Sunday, only the Derry Bloody Sunday (January 30, 1972)  There were a lot of bloody days during the Irish Civil War.  What a terrible mess.