The Irish Republican Army (IRA; Irish: Óglaigh na hÉireann) was an Irish republican revolutionary paramilitary organisation who waged a guerrilla campaign against the British occupation of Ireland in the 1919–1921 Irish War of Independence. It was descended from the Irish Volunteers, an organisation established on 25 November 1913 that staged the Easter Rising in April 1916. In 1919, the Irish Republic that had been proclaimed during the Easter Rising was formally established by an elected assembly (Dáil Éireann), and the Irish Volunteers were recognised by Dáil Éireann as its legitimate army.
Following the signing in 1921 of the Anglo-Irish Treaty, which ended the War of Independence, a split occurred within the IRA. Members who supported the treaty formed the nucleus of the Irish National Army. However, most of the IRA was opposed to the treaty. The anti-treaty IRA fought a civil war against the Free State Army in 1922–1923, with the intention of creating a fully independent all-Ireland republic. Having lost the civil war, this group remained in existence, with the intention of overthrowing the governments of both the Irish Free State and Northern Ireland and achieving the Irish Republic proclaimed in 1916.
This organisation was the ancestor of many groups also known as the Irish Republican Army, and distinguished from them as the Old IRA.
The Irish Volunteers, founded in 1913, staged the Easter Rising, which aimed at ending British rule in Ireland, in 1916. Following the suppression of the Rising, thousands of Volunteers were imprisoned or interned, leading to the break-up of the organisation. It was reorganised in 1917 following the release of first the internees and then the prisoners. At the army convention held in Dublin in October 1917, Éamon de Valera was elected president, Michael Collins Director for Organisation and Cathal Brugha Chairman of the Resident Executive.
Following the success of Sinn Féin in the 1918 general election and the setting up of the First Dáil (the legislature of the Irish Republic), Volunteers commenced military action against the Royal Irish Constabulary (RIC), the paramilitary police force in Ireland, and subsequently against the British Army. It began with the Soloheadbeg Ambush, when members of the Third Tipperary Brigade led by Séumas Robinson, Seán Treacy, Dan Breen and Seán Hogan, seized a quantity of gelignite, killing two RIC constables in the process.
The Dáil leadership worried that the Volunteers would not accept its authority, given that, under their own constitution, they were bound to obey their own executive and no other body. In August 1919, Brugha proposed to the Dáil that the Volunteers be asked to swear allegiance to the Dáil, but one commentator states that another year passed before the movement took an oath of allegiance to the Irish Republic and its government in "August 1920". In sharp contrast, a contemporary in the struggle for Irish independence notes that by late 1919, the term "Irish Republican Army (IRA)" was replacing "Volunteers" in everyday usage. This change is attributed to the Volunteers, having accepted the authority of the Dáil, being referred to as the "army of the Irish Republic", popularly known as the "Irish Republican Army". Already in September 1917, a group of men from counties Clare and Tipperary charged with illegal drilling were claiming to be soldiers of the "Irish Republican Army". They refused to recognise the legitimacy of the court and insisted they be treated as prisoners of war.
A power struggle continued between Brugha and Collins, both cabinet ministers, over who had the greater influence. Brugha was nominally the superior as Minister for Defence, but Collins's power base came from his position as Director of Organisation of the IRA and from his membership on the Supreme Council of the Irish Republican Brotherhood (IRB). De Valera resented Collins's clear power and influence, which he saw as coming more from the secretive IRB than from his position as a Teachta Dála (TD) and minister in the Aireacht. Brugha and de Valera both urged the IRA to undertake larger, more conventional military actions for the propaganda effect but were ignored by Collins and Mulcahy. Brugha at one stage proposed the assassination of the entire British cabinet. This was also discounted due to its presumed negative effect on British public opinion. Moreover, many members of the Dáil, notably Arthur Griffith, did not approve of IRA violence and would have preferred a campaign of passive resistance to the British rule. The Dáil belatedly accepted responsibility for IRA actions in April 1921, just three months before the end of the Irish War of Independence.
In practice, the IRA was commanded by Collins, with Richard Mulcahy as second in command. These men were able to issue orders and directives to IRA guerrilla units around the country and at times to send arms and organisers to specific areas. However, because of the localised and irregular character of the war, they were only able to exert limited control over local IRA commanders such as Tom Barry, Liam Lynch in Cork and Seán Mac Eoin in Longford.
The IRA claimed a total strength of 70,000, but only about 3,000 were actively engaged in fighting against the Crown. The IRA distrusted those Irishmen who had fought in the British Army during the First World War as potential informers, but there were a number of exceptions such as Emmet Dalton, Tom Barry and Martin Doyle. The IRA divided its members into three classes, namely "unreliable", "reliable" and "active". The "unreliable" members were those who were nominally IRA members but did not do very much for the struggle, "reliable" members played a supporting role in the war while occasionally fighting and the "active" men those who were engaged in full-time fighting. Of the IRA brigades only about one to two-thirds were considered to be "reliable" while those considered "active" were even smaller. A disproportionate number of the "active" IRA men were teachers, medical students, shoemakers and bootmakers; those engaged in building trades like painters, carpenters and bricklayers; draper's assistants and creamery workers. The Canadian historian Peter Hart wrote "...the guerrillas were disproportionately skilled, trained and urban". Farmers and fishermen tended to be underrepresented in the IRA. Those Irishmen engaged in white-collar trades or working as skilled labourers were much more likely to be involved in cultural nationalist groups like the Gaelic League than farmers or fishermen and thus to have a stronger sense of Irish nationalism. Furthermore, the authority of the Crown tended to be stronger in towns and cities than in the countryside. Thus, those engaged in Irish nationalist activities in urban areas were much more likely to come into conflict with the Crown, leading to a greater chance of radicalisation. Finally, the British tactic of blowing up the homes of IRA members had the effect of discouraging many farmers from joining the struggle as the destruction of the family farm could easily reduce a farmer and his family to destitution. Of the "active" IRA members, three-quarters were in their late teens or early 20s and only 5% of the "active" men were in the age range of 40 or older. The "active" members were overwhelmingly single men with only 4% being married or engaged in a relationship. The life of an "active" IRA man with the stress of living on the run and constantly being in hiding tended to attract single men who could adjust to this lifestyle far more easily than a man in a relationship. Furthermore, the IRA preferred to recruit single men as it was found that singles could devote themselves more wholeheartedly to the struggle.
Women were active in the republican movement, but almost no women fought with the IRA whose "active" members were almost entirely male. The IRA was not a sectarian group and went out of its way to proclaim it was open to all Irishmen, but its membership was largely Catholic with virtually no Protestants serving as "active" IRA men. Hart wrote that in his study of the IRA membership that he found only three Protestants serving as "active" IRA men between 1919 and 1921. Of the 917 IRA men convicted by British courts under the Defence of the Realm Act in 1919, only one was a Protestant. The majority of those serving in the IRA were practising Catholics, but there was a large minority of "pagans" as atheists or non-practising Catholics who were known in Ireland. The majority of the IRA men serving in metropolitan Britain were permanent residents with very few sent over from Ireland. The majority of the IRA men operating in Britain were Irish-born, but there was a substantial minority who were British-born, something that made them especially insistent on asserting their Irish identity.