A fourth, senior officer - who should have been overseeing the operation - was forced to drive the van.
Portlaoise Prison is carrying out an internal investigation after a three officers were too drunk to escort a prisoner back from Dublin.
The incident, which occurred earlier this month, involved the escort a dangerous gangland criminal from the Criminal Courts of Justice.
A fourth, senior officer - who should have been overseeing the operation - was forced to drive the van, after the three junior officers spent part of the day drinking.
The van also stopped for a toilet break at the Junction 14 service station on the M7 - which is strictly prohibited while carrying a prisoner - and the three junior officers also attended the fast food outlet on site.
The incident came to the attention of management upon their return.
However, Special Correspondent with the Irish Examiner, Mick Clifford doesn't expect there will be major disciplinary action: