the ambush was organised by tom barry and the IRA they used guerilla warfare and flying collums. after the ambush the men escaped to shanacashel safe houses

-Cause of the burning of Cork, Irishhistory.com

It began on the Dec 11 , 1920.

57 buildings were completely destroyed by fire, 20 buildings were badly damaged and 12 were wrecked and looted. 2000 people lost their jobs, and £2.5 million worth of damage was done. 

Michael Collins ordered the launch of a concentrated series of arson attacks on hundreds of abandoned police barracks with a view to preventing them from being reoccupied. 

Around 4pm, a scout reported that it left Kinsale but had turned back. When Barry received this report, he stood down the column and moved it to billets in Skeugh, east of Innishannon.

Barry believed that since the column had mobilised, it was important for the men to undertake an operation. When he discussed the situation with his officers the following day, Liam Deasy stated that British lorries had passed through Crossbarry earlier that week and, as the column was close to the village.
Barry’s calculation was that his men, who had only 40 rounds each, could not sustain the all-day fight that they could expect if they retired before the British. He observed, however, that one of the British columns advancing towards Crossbarry was well ahead of the other enemy units. If his men could break through this British force, roughly the same strength as his own, they could break out of the encirclement.