During the troubles and particularly in the 1970s border security was undertaken by unarmed Garda backed up units of the Irish Army. In particular, after the bombing and assassinations in border areas by loyalist gangs run by the British Army, generally Garda checkpoints were a few miles ‘south’ manned by Garda and a platoon of Infantry. Some main crossings for example Blacklion, Lifford etc did have permanent Irish Army checkpoints for a time.
The Irish Army’s ability to meet a border security role was however severely compromised about a decade ago when its 4th Brigade HQ in Athlone was closed down. It had coordinated operations over 10 counties, including Connaught, the Leinster Midlands and the Ulster Counties of Donegal and Cavan, with 263km of the border.