Violence escalated steadily from that summer and sharply after November 1920 until July 1921. (It was in this period that a mutiny broke out among the Connaught Rangers, stationed in India. Two were killed whilst trying to storm an armory and one was later executed).
About 300 people had been killed by late 1920, but the conflict escalated in November. On Bloody Sunday in Dublin, 21 November 1920, fourteen British intelligence operatives were assassinated in the morning; then in the afternoon the RIC opened fire on a crowd at a Gaelic football match, killing fourteen civilians and wounding 65. A week later, seventeen Auxiliaries were killed by the IRA in the Kilmichael Ambush in County Cork.
Then, on 21 November 1920, there was a day of dramatic bloodshed in Dublin. In the early morning, Collins' Squad attempted to wipe out the leading British intelligence operatives in the capital. The Squad shot 19 people, killing 14 and wounding 5. These consisted of British Army officers, police officers and civilians. The dead included members of the Cairo Gang and a courts-martial officer, and were killed at different places around Dublin.
On 28 November 1920, only a week after Bloody Sunday in Dublin, the west Cork unit of the IRA, under Tom Barry, ambushed a patrol of Auxiliaries at Kilmichael in County Cork, killing all but one of the 18-man patrol.