 Coen joined the IRA and served with the Sligo Brigade and was a member of the Southern Command.In 1971, Coen was imprisoned in Mountjoy Prison, Dublin, where he was jailed with fellow Republican Dan Hoban.At the age of 28, Coen was killed by a British Army soldier while on active service at Cassidy's Cross (also known as Mullan Cross) near Kinawley, a village in the south-west of County Fermanagh in Northern Ireland, close to the County Cavan / County Fermanagh border, on 20 January 1975.