The first regiment of the Irish National Army, sometimes unofficially referred to as the Free State army or the Regulars, is set up in Dublin on January 31, 1922.

The National Army is the army of the Irish Free State from January 1922 until October 1924. Its role in this period is defined by its service in the Irish Civil War, in defence of the institutions established by the Anglo-Irish Treaty. Michael Collins is the army’s first chief of staff from its establishment until his death in an ambush at Béal na mBláth on August 22, 1922.

The National Army is constituted from the revolutionary Irish Republican Army (IRA), which emerges from the successful Irish War of Independence fought as a guerrilla campaign against the British Army and Royal Irish Constabulary. Its first troops are those IRA volunteers who support the Anglo-Irish Treaty and the Provisional Government of Ireland formed there under. The army makes its first public appearance on January 31, 1922, when command of Beggars Bush Barracks is handed over from the British Army.

Conflict arises between the National Army and the anti-Treaty components of the IRA, which does not support the government of the Irish Free State. On June 28, 1922 the National Army commences an artillery bombardment of anti-Treaty IRA forces who are occupying the Four Courts in Dublin, thus beginning the Irish Civil War.

The National Army is greatly expanded in size to fight the civil war against the anti-Treaty IRA, in a mostly counter-insurgency campaign that is brought to a successful conclusion in May 1923. From October 1, 1924, the Army is reorganised into a smaller, better regulated force. The term “National Army” is superseded by the legal establishment of the Defence Forces as the Irish Free State’s military force.