April 1971, after the arrest and imprisonment of Billy McKee, Cahill became the commander of the Provisional IRA Belfast Brigade. He held this post until the introduction of internment in August of that year. It was during this period that the Provisional IRA campaign got off the ground in the city. Cahill authorised the beginning of the IRA's bombing campaign as well as attacks on British troops and the RUC. He based himself in a house in Andersonstown and toured the city, co-ordinating IRA activity. The day after the British Army mounted Operation Demetrius, designed to arrest the IRA's leaders, Cahill held a press conference in a school in Ballymurphy and stated that the operation had been a failure. He said, "we have lost one brigade officer, one battalion officer and the rest are volunteers, or as they say in the British Army, privates". To avoid the propaganda defeat that his capture would then have entailed, Cahill fled to the Republic of Ireland, temporarily relinquishing his command of the Belfast Brigade. In March 1972, Cahill was part of an IRA delegation that held direct talks with the British Labour Party leader Harold Wilson. However, although the IRA called a three-day ceasefire for the talks, no permanent end to violence was agreed upon. Upon his return to Ireland, Cahill was arrested in Dublin by Gardaí and charged with IRA membership. He went on hunger strike for twenty-three days and was subsequently released due to lack of evidence. In November 1972, Cahill became the IRA's chief of staff and held this position until his arrest the following year. Cahill was then put in charge of importing arms for the IRA. He liaised with the NORAID group in America and with the Libyan dictatorship of Muammar al-Gaddafi to this end. On March 29, 1973 he was arrested by the Irish Navy in Waterford, aboard the Claudia, a ship from Libya loaded with five tons of weapons. Cahill was sentenced to three years imprisonment by the Irish Special Criminal Court. Cahill stated at his trial that, "If I am guilty of any crime, it is that I did not succeed in getting the contents of the Claudia into the hands of the freedom fighters in this country". Upon his release, Cahill again was put in charge of arms importation and to this end went to the United States. He was deported from the United