In May and June 1922, Collins launched a guerrilla IRA offensive against Northern Ireland. By this time, the IRA was split over the Anglo-Irish Treaty, but both pro and anti-treaty units were involved in the operation. Some of the arms sent by the British to arm the new Irish Army were in fact given to IRA units and their weapons sent to the North. However, the offensive, launched with a series of IRA attacks in the North on 17–19 May, ultimately proved a failure. An IRA Belfast Brigade report in late May concluded that continuing the offensive was "futile and foolish...the only result of the attack was to place the Catholic population at the mercy of the Specials".