Belfast Brigade ( Irish Republican Army ) The Belfast Brigade of the Irish Republican Army ( IRA ) was formed in March 1921 during the Irish War of Independence , when the IRA was re - organised by its leadership in Dublin into Divisions and Joe McKelvey was appointed commander of the Third Northern Division , responsible for Belfast and the surrounding area . There were three battalions within the Brigade , the 1st in West Belfast , the 2nd in North Belfast and the Third in East Belfast . Most of the Brigades attacks on Crown forces were carried out by an Active Service Unit within the 1st battalion , led by Roger McCorley . The Brigade was strengthened during the period between the end of hostilities between the IRA and British forces in July 1921 and the outbreak of the Irish Civil War in June 1922 . During this time , Michael Collins , head of the new Irish Free State sent arms and money to the IRA in Belfast in an effort to de - stabilise the newly created Northern Ireland . By May 1922 , the IRA in Belfast possessed over 600 rifles . They carried out many attacks on British and Northern Ireland force during this period . In addition , they were often faced with the task of trying to defend Catholic areas of Belfast from attack by loyalist and state forces . As well as defence , though , the Brigade was also guilty of sectarian attacks , including assassinations of Protestants and the bombing of trams taking Protestant workers to work - places that had expelled Catholics . In May 1922 , the IRA in Belfast assassinated Unionist MP William Twaddell . In response , the next day , the Unionist government interned over 200 Republicans in Belfast and 350 throughout Northern Ireland . Over 750 IRA men were interned by 1923 . This was a damaging blow to the Belfast Brigade , but more damaging still was the outbreak of the Irish Civil War on June 28 . This meant that the IRA in the south of Ireland was now split into warring factions . In addition , the aid which the Free State government had given to the northern IRA was cut off after the death of Michael Collins in August 1922 . On top of this , Joe McKelvey , the leader of the IRA in Belfast , left the city to side with te Anti - Treaty IRA in the civil war . He was captured and subsequently executed by the Free State . Most of the other IRA leaders in Belfast supported the Anglo - Irish Treaty , as they had been persuaded that it would ultimately result in a united , independent Ireland . In addition over 1000 IRA men in Belfast had to flee Northern Ireland to escapethe repression there and around 500 of them were recruited into the pro - treaty National Army during the civil war . As a result of these factors , the IRA in Belfast was all but destroyed in this period and was unable to mount a threat to British rule in Northern Ireland for many years . The organisation carried out some shootings in Belfast in the 1940s , for which a number of their members were hanged . In the IRA Border Campaign of the 1950s , there were no actions in Belfast . It took the formation of the Provisional IRA and its Belfast Brigade in 1969 before republicans were again in a position to carry out attacks in Northern Ireland ' s capital city . The IRA of the 1920s in Belfast is the subject of the song Belfast Brigade .