Inside the building were 12 members of the Irish Republican Army Executive, including Chief-of-Staff Joe McKelvey, Director of Engineering Rory O'Connor and Quartermaster General Liam Mellows.
The garrison consisted of roughly 180 men drawn from the 1st and 2nd Battalions of the IRA's 1st Dublin Brigade, commanded by Commandant Paddy O'Brien, armed for the most part only with small arms (rifles, five Thompson submachineguns and two Lewis light machine guns) apart from one captured armored car, which they named "The Mutineer".
The members of the IRA Army Executive were the political leaders of the garrison, but served as common soldiers under the command of Ernie O'Malley, commander of the IRA's 2nd Southern Division.
The Anti-Treaty side fortified the Four Courts to some extent, planting mines around the complex and barricading the doors and windows, but their leadership ordered them not to fire first, in order to retain the moral high ground, and so the Free State troops were allowed to surround the Four Courts.

After the first day's bombardment proved ineffective, the British gave the Free State two more 18-pounder cannon and proffered 60-pounder howitzers along with an offer to bomb the Four Courts from the air.
Collins turned down the latter two offers because of the risk of causing heavy civilian casualties.
On the 29th, Free State troops stormed the eastern wing of the Four Courts, losing three killed and 14 wounded and taking 33 prisoners.
The republicans' armored car, "The Mutineer", was disabled and abandoned by its crew.
Early the next day Paddy O'Brien was injured by shrapnel and Ernie O'Malley took over military command in the Four Courts.
By this time the shelling had caused the Four Courts to catch fire.
In addition, orders arrived from Oscar Traynor, the anti-treaty IRA commander in Dublin, for the Four Courts garrison to surrender, as he could not reach their position to help them.
At 3:30 p.m. on 30 June, O'Malley surrendered the Four Courts to Brig.
Gen. Paddy Daly of the Free State's Dublin Guard unit.
Three of the republican garrison had died in the siege
Inside the building were 12 members of the Irish Republican Army Executive, including Chief-of-Staff Joe McKelvey, Director of Engineering Rory O'Connor and Quartermaster General Liam Mellows. The garrison consisted of roughly 180 men drawn from the 1st and 2nd Battalions of the IRA's 1st Dublin Brigade, commanded by Commandant Paddy O'Brien, armed for the most part only with small arms (rifles, five Thompson submachineguns and two Lewis light machine guns) apart from one captured armored car, which they named "The Mutineer". The members of the IRA Army Executive were the political leaders of the garrison, but served as common soldiers under the command of Ernie O'Malley, commander of the IRA's 2nd Southern Division. The Anti-Treaty side fortified the Four Courts to some extent, planting mines around the complex and barricading the doors and windows, but their leadership ordered them not to fire first, in order to retain the moral high ground, and so the Free State troops were allowed to surround the Four Courts.
After the first day's bombardment proved ineffective, the British gave the Free State two more 18-pounder cannon and proffered 60-pounder howitzers along with an offer to bomb the Four Courts from the air. Collins turned down the latter two offers because of the risk of causing heavy civilian casualties. On the 29th, Free State troops stormed the eastern wing of the Four Courts, losing three killed and 14 wounded and taking 33 prisoners. The republicans' armored car, "The Mutineer", was disabled and abandoned by its crew. Early the next day Paddy O'Brien was injured by shrapnel and Ernie O'Malley took over military command in the Four Courts. By this time the shelling had caused the Four Courts to catch fire. In addition, orders arrived from Oscar Traynor, the anti-treaty IRA commander in Dublin, for the Four Courts garrison to surrender, as he could not reach their position to help them. At 3:30 p.m. on 30 June, O'Malley surrendered the Four Courts to Brig. Gen. Paddy Daly of the Free State's Dublin Guard unit. Three of the republican garrison had died in the siege
Battle of Dublin