Anti-Treaty commander in the Four Courts, Paddy O’Brien is wounded by shrapnel. Ernie O’Malley assumes command. In the morning there is a truce to remove the wounded. Shortly afterward, a massive explosion destroys the western wing of the Four Courts and the Irish Public Records Office along with it. Forty advancing Free State troops were seriously injured. It was alleged by the National Army Headquarters that the Anti-treaty forces deliberately booby-trapped the Public Record office to kill Free State troops. Tim Healy, a government supporter, later alleged that the explosion was the result of land-mines laid before the surrender, which exploded after the surrender. However, a study of the battle concluded that the explosion was caused by fires ignited by the shelling of the Four Courts, which eventually reached two truck loads of gelignite in the munitions factory. A towering mushroom cloud rose 200 feet over the Four Courts.
Ernie O’Malley surrendered the Four Courts when Oscar Trayner sent word that he could not break through to help them. Three of the republican garrison had died in the siege. Liam Mellows, Rory O’Connor, Joe McKelvey and Dick Barret were among the prisoners; Ernie O’Malley and Seán Lemass escaped from captivity to continue fighting elsewhere.
Notably, the shelling of the Four Courts and the ferocity of the fighting around the rest of Dublin during the initial phase of the war showed that neither side would balk at killing former friends if that was what was required.
Photo Ernie O’Malley, colourised by 1916 Easter Revolution in Colour