In 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. 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 States in 1984 for
illegal entry (see
Provisional IRA arms importation). He served on the
IRA Army Council as late as the 1990s. In the late 1970s and early 1980s, he argued against proposals for
Sinn Féin to stand in elections. However, in 1985, he spoke at the party's
Ard Fheis in favour of republicans contesting elections and taking seats in the Dublin parliament, the
Dáil. ==Peace process==