Bloody Sunday

Father Edward Daly, waving a blood-stained white handkerchief as he escorts a mortally-wounded protester to safety during the events of Bloody Sunday (1972) in Derry, Northern Ireland.

January 30, 1972:

Bloody Sunday (Irish: Domhnach na Fola)—sometimes called the Bogside Massacre—was an incident on 30 January 1972 in the Bogside area of Derry, Northern Ireland, in which 26 unarmed civil-rights protesters and bystanders were shot by soldiers of the British Army. Thirteen males, seven of whom were teenagers, died immediately or soon after, while the death of another man four-and-a-half months later was attributed to the injuries he received on that day. Two protesters were also injured when they were run down by army vehicles. Five of those wounded were shot in the back. The incident occurred during a Northern Ireland Civil Rights Association march; the soldiers involved were members of the First Battalion of the Parachute Regiment (1 Para).
Two investigations have been held by the British government. The Widgery Tribunal, held in the immediate aftermath of the event, largely cleared the soldiers and British authorities of blame—Widgery described the soldiers' shooting as "bordering on the reckless"—but was criticised as a "whitewash", including by Jonathan Powell. The Saville Inquiry, chaired by Lord Saville of Newdigate, was established in 1998 to reinvestigate the events. Following a 12-year inquiry, Saville's report was made public on 15 June 2010, and contained findings of fault that could re-open the controversy, and potentially lead to criminal investigations for some soldiers involved in the killings. The report found that all of those shot were unarmed, and that the killings were both "unjustified and unjustifiable." On the publication of the Saville report the British prime minister, David Cameron, made a formal apology on behalf of the United Kingdom.
The Provisional Irish Republican Army's (IRA) campaign against the partition of Ireland had begun in the two years prior to Bloody Sunday, but public perceptions of the day boosted the status of, and recruitment into, the organisation enormously. Bloody Sunday remains among the most significant events in the Troubles of Northern Ireland, chiefly because it was carried out by the army and not paramilitaries, in full view of the public and the press.

The Troubles had already been going on for a couple of years, but this British Army clusterfuck caused all hell to break loose.