A major garda operation has been launched over fears Isis could use Irish ports to begin an attack.
Security at Dublin and Rosslare was deemed to be "weak" and armed officers are now patrolling the ports in a bid to stop Islamic State (IS) suspects from using Ireland as easy access to the UK.
The investigation - codenamed Operation Mutiny - has resulted in garda activity at Dublin and Rosslare being massively stepped up in recent weeks.
Sources revealed that the operation was put in place after high-level meetings between senior garda detectives and their UK counterparts after the summer Brexit referendum in which the UK voted to withdraw from the European Union.
Garda management decided to offer vast amounts of overtime to officers who were willing to work extra hours in the capital's port as well as at Rosslare in Co Wexford.
It is understood that in Rosslare alone, garda management have sanctioned 100 hours of overtime a day as part of the ongoing investigation.
"Security at our ports was found to be porous and weak. The UK authorities were very concerned that IS terrorists could use these ports to get into Britain to launch a terrorist attack so Operation Mutiny was put in place," a source told the Herald.
"There were a number of meetings held between representatives of the different forces and these ultimately led to the drawing up of a policing plan which has been successful so far," the source added.
"This has been a sustained and massive operation which has meant that gardai have been checking virtually every vehicle coming into and out of these ports," a source said.
"Overtime for officers is being offered on a daily basis and there can be no doubt that these ports are far more secure than they were even a couple of months ago," the source added.
Apart from regular garda units, the policing of the ports has led to a significant heavily armed garda presence from the Garda Regional Support Unit (RSU). The RSU, based in the Southern Region, has even been deployed in Rosslare when armed officers from the South East have been unavailable.
While no IS terrorists have yet been intercepted, gardai have made a number of "significant seizures" of stolen property.
In particular, members of Romanian and other Eastern European organised crime gangs have been arrested on a number of occasions with vehicles full of stolen goods suspected to have been taken in burglaries across Ireland.
Port searches of vehicles as part of Operation Mutiny have also led to the seizure of "numerous" stolen car parts which were being smuggled out of the country.
Despite its successes, it is understood Operation Mutiny is due to be "wound down" before the end of the year.