Despite containing several brutal scenes of violence, the film was given a very lenient 'PG' rating in Ireland mainly because of its historical context. The censor issued a press statement defending his decision claiming the film was a landmark in Irish cinema and that he believed "because of the subject matter, parents should have the option of making their own decision as to whether their children should see the film or not". The Film subsequently became the second most successful movie ever released in Ireland.
The character Ned Broy, played by Stephen Rea in the film, is in fact a composite of the historical figures Ned Broy, who was a double agent in the police, and Dick McKee, who was Commandant of the Dublin Brigade of the IRA and hence a central figure in planning intelligence operations with Collins. Broy survived the war, but McKee was captured the night before the attack on British agents and shot, reputedly whilst attempting to escape. Broy, only a Sergeant in the Dublin Metropolitan Police would be rewarded by being made head of the Irish Free State's new police national force, the Garda. Ironically he would go to great lengths to encourage ex-Royal Irish Constubulary officers to join the new force, giving them preference in recruitment and absorb the Dublin Metropolitan Police as a whole into the new organisation.
Director Jordan shows an armored vehicle with a machine gun turret shooting at players and spectators during the Croke Park Massacre in Dublin during a Gaelic Football match. In reality the Royal Irish Constabulary only used trucks and rifles.
The trivia items below may give away important plot points.
The later-on released DVD was flippable and had two sides, much like an old LP. In one of the first scenes, Michael Collins fought along with the rebellion against the military. After you flip over the DVD, the first scene shown is Collins now on the military side fighting against the new-formed rebellion. The side-change of the DVD dramatically marks the change of Collins' position.
This film did not show Eamon De Valera order the assignation of Collins but it does insinuate he ordered it. This has been a highly contentious issue in Ireland for decades; although De Valera is widely believed to have ordered the murder he denied it ever since.