On July 30, 1919, the first assassination authorised by Michael Collins is carried out by The Squad, also known as the Twelve Apostles, when Detective Sergeant “the Dog” Smith is shot near Drumcondra, Dublin.

The Squad is an Irish Republican Army (IRA) unit founded by Collins to counter British intelligence efforts during the Irish War of Independence, mainly by means of assassination.

On April 10, 1919, the First Dáil announces a policy of ostracism of Royal Irish Constabulary (RIC) men. At the time Sinn Féin official policy is against acts of violence. Boycotting, persuasion and mild intimidation succeed against many officers. However others escalate their activities against republicans and in March 1920 Collins asks Dick McKee to select a small group to form an assassination unit.

When The Squad is formed, it comes directly under the control of the Director of Intelligence or his deputy and under no other authority. The Squad is commanded by Mick McDonnell.

The original “Twelve Apostles” are Mick McDonnell, Tom Keogh, Jimmy Slattery, Paddy Daly, Joe Leonard, Ben Barrett, Vincent Byrne, Sean Doyle, Paddy Griffin, Eddie Byrne, Mick Reilly and Jimmy Conroy. After some time The Squad is strengthened with members Ben Byrne, Frank Bolster, Mick Keogh, Mick Kennedy, Bill Stapleton and Sam Robinson. Owen Cullen, a member of 2nd Battalion, is driver for a short time, and Paddy Kelly of County Clare for a short time. They are employed full-time and received a weekly wage.

Sometimes, as occasion demands, The Squad is strengthened by members of the IRA Intelligence Staff, the Active Service Unit, munition workers and members of the Dublin Brigade, Tipperary Flying Column men, Dan Breen, Séumas Robinson, Seán Treacy and Seán Hogan, and also Mick Brennan and Michael Prendergast of County Clare. The IRA Intelligence Staff consists of the Director of Intelligence Michael Collins, the Deputy Director of Intelligence Liam Tobin, the Second Deputy Director of Intelligence Tom Cullen, the Third Director of Intelligence Frank Thornton, and members Joe Dolan, Frank Saurin, Ned Kelleher, Joe Guilfoyle, Paddy Caldwell, Paddy Kennedy, Charlie Dalton, Dan McDonnell and Charlie Byrne. The munitions workers include Mat Furlong, Sean Sullivan, Gay McGrath, Martin O’ Kelly, Tom Younge and Chris Reilly.

Other members include Mick Love, Gearoid O’Sullivan, Patrick Caldwell, Charlie Dalton, Mick O’Reilly, Sean Healy, James Ronan, Paddy Lawson, John Dunne, Johnny Wilson and James Heery. Seán Lemass and Stephen Behan, the father of Irish writers Brendan and Dominic Behan, have also been listed as members of the Apostles. There is no hard evidence to support the inclusion of many of the names, but those who subsequently serve in the Irish Army have their active service recorded in their service records held in the Military Archives Department in Cathal Brugha Barracks, Rathmines. Andrew Cooney is also reported to have been associated with The Squad. Stephen Behan’s involvement is first made public in 1962, when the BBC broadcasts an episode of This Is Your Life dedicated to Behan. During the broadcast, remaining members of the squad joined Behan on the set of the show.

Following “The Dog” Smith’s assassination, The Squad continues to target plainclothes police, members of the G Division of the Dublin Metropolitan Police, and, occasionally, problematic civil servants. Organisationally it operates as a subsection of Collins’ Intelligence Headquarters. Two of the executions by The Squad are the killing on January 21, 1920 of RIC Inspector William Redmond of the DMP “G” Division and on March 2, 1920 a British double agent John Charles Byrnes.

One of the Apostles’ particular targets is the Cairo Gang, a deep-cover British intelligence group, so called since it has either been largely assembled from intelligence officers serving in Cairo or from the Dublin restaurant called The Cairo, which the gang frequents. Sir Henry Wilson brings in the Cairo Gang in the middle of 1920, explicitly to deal with Michael Collins and his organization. Given carte blanche in its operations by Wilson, the Cairo Gang adopts the strategy of assassinating members of Sinn Féin unconnected with the military struggle, assuming that this will cause the IRA to respond and bring its leaders into the open.

The most well-known operation executed by the Apostles occurs on what becomes known as Bloody Sunday, November 21, 1920, when British MI5 officers, linked to the Cairo Gang and significantly involved in spying, are shot at various locations in Dublin with fourteen killed and six wounded. In addition to the The Squad, a larger number of IRA personnel are involved in this operation. The only IRA man captured during the operation is Frank Teeling. In response to the killings, the Black and Tans retaliate by shooting up a Gaelic football match between Dublin and Tipperary at Croke Park, the proceeds from which are for the Irish Republican Prisoners Fund. Fourteen civilians are killed including one of the players, Michael Hogan, and 68 are wounded. The Hogan stand at Croke Park is named after Hogan.

The elimination of the Cairo Gang is seen in Dublin as an intelligence victory, but British Prime Minister David Lloyd George comments dismissively that his men “… got what they deserved, beaten by counter-jumpers…”. Winston Churchill adds that they were “.. careless fellows … who ought to have taken precautions.”

Some members of The Squad are hanged in 1921 for the killings on Bloody Sunday, including Thomas Whelan and Patrick Moran. Moran had killed a vet, Patrick MacCormack, who seems to have been an innocent victim.

In May 1921, after the IRA’s Dublin Brigade takes heavy casualties during the burning of the Custom House, The Squad and the Brigade’s Active Service Unit are amalgamated into the Dublin Guard, under Paddy Daly. Under the influence of Daly and Michael Collins, most of the Guard take the Free State side and join the National Army in the Irish Civil War of 1922–23. During this conflict some of them are attached to the Criminal Investigation Department and are accused of multiple assassinations of Anti-Treaty fighters. They are also involved in several atrocities against Republican prisoners, particularly after the death of Collins, due to many of them having personal ties with him.

Bill Stapleton goes on to become a director in Bord na Móna, Charles Dalton and Frank Saurin become directors in the Irish Sweepstakes. In October 1923, Commandant James Conroy is implicated in the murder of two Jewish men, Bernard Goldberg and Emmanuel ‘Ernest’ Kahn. He avoids arrest by fleeing to Mexico, returning later to join the Blueshirts. A later application for an army pension is rejected. The killings are the subject of a 2010 investigative documentary by RTÉ, CSÍ: Murder in Little Jerusalem.