Joint Northern Ireland Offensive
According to Hopkinson, the roots of this planned offensive were in efforts by Collins and Lynch (and other IRB men) to maintain IRA unity. After failure of second Collins-Craig pact, plans were laid to transport north a large consignment of arms. Guns given to the Provisional Government by the British were given to the Anti-Treaty units who were to transport their arms north so as avoid detection of their origin. A number of volunteers (Macardle says 100) were also to go north with Sean Lehane from Cork taking over as O/C of 1st Northern Division (mostly Donegal) and 2nd Northern Division (mostly Derry and Tyrone) with Charlie Daly as his second in command. On the 19th May, some attacks did take place in the 3rd Northern Division area (Antrim and East Down) with the burnings of Shane's Castle in Co Antrim; Edencourt Castle on Carlingford Lough and Glenmona. There was widespread burning in Belfast and Ballymena railway station was burned. Phoenix says that there was general activity through-out the 3rd Northern Division area with attacks on police barracks, ancestral homes and railways. At least five stately homes damaged. On the 19th, at least seven business premises torched in Belfast (including Doran & Co. on Donegall Quay) and another eleven businesses in the city attacked on the 20th. On the 21st, further businesses were targeted including Ferguson’s motor works on May St. and the Carnigie Library on the Falls Road. There were numerous hoaxes which stretched the city’s fire brigades.
It would seem that after the failure of the attack on Musgrave St police barracks, orders were given to call of the planned attacks. However, this did not stop officers from the 3rd Northern complaining of lack of activity by the other northern divisions. Indeed, Woods later explained to Mulcahy that he had to call off operations because the inaction of other divisions led to a great increase in his enemy forces in his area. It would seem that other divisions were not brought into action but because of a deliberate decision by the pro-Treaty army leadership due to the reaction of the British to the Collins-de Valera pact. (Pro- and Anti-IRA units had an armed clash in Newtowncunningham in Co. Donegal.)
However, Phoenix says that the co-ordinated IRA attacks led NI Government to unleash a terrible sectarian backlash against Belfast Catholics with 12 Catholics being killed over the 20th and 21st May and mob attacks on Catholic areas. McDermott noted that the “failure of the May/June offensive severely disrupted the IRA in Belfast and no section of the organisation was particularly active after August 1922” (McDermott (2001), pg 257).
Hopkinson points out that this joint IRA offensive is a "sensitive and controversial subject because of the mistrust, secrecy and confusion involved, and its virtually total failure" (Hopkinson (1988), pg 83). It was also sensitive because of duplicity involved on Collins' behalf. However, the British found out about pro-Treaty involvement through captured documents and the public disagreements that broke out after the failure of the offensive. The British chose to turn a blind eye. Phoenix suggests that practically all IRA activity in the North was carried out by pro-Treaty forces (as practically all IRA in the North had gone pro-Treaty).