"Take it Down from the Mast" is an Irish Republican song originally written in 1923 by James Ryan, and published in Leslie Daiken's collection Good-Bye, Twilight: Songs of Struggle in Ireland in 1936, entitled "Lines Written by an Irish Soldier in 1923". Its lyrics refer to the Irish Civil War (1922–23).
In the 1950s a version written by Dominic Behan specifically referred to the judicial murder of four members of the IRA Executive—Dubliner Rory O'Connor, who had commanded the Four Courts garrison at the outbreak of the Civil War, Galway Republican Liam Mellows, Cork republican Richard Barrett and Tyrone republican officer Joseph McKelvey. Their execution was a reprisal for the IRA's murder of Sean Hales, TD the day before, December 7, 1922.
The flag in question is the Irish tricolour, which the song tells supporters of the Anglo-Irish Treaty and the Irish Free State to take down, as it is the flag of the Irish Republic, which the "Free Staters" betrayed.
At the time, the Anti-Treaty IRA regarded their Civil War opponents as traitors and therefore unworthy to use the Irish tricolour.