 In the War of Independence (1919–21, he was the Adjutant of the 3rd Cork Brigade (West Cork).He served under Tom Barry in one of the unit's best known action, the Crossbarry Ambush in March 1921.His younger brother, Pat, died in action at the Kilmichael Ambush in November 1920, an engagement which Liam Deasy himself was not present at.