A suspected €80m worth of cocaine was seized by the Naval Service after an armed team boarded a yacht off the Cork coast.
The operation by the Naval Service, Gardai and Customs & Excise followed a lengthy intelligence mission in which Irish agencies co-operated with UK, European and north American police forces.
It is believed the drugs were destined for the UK and European markets rather than for Ireland.
The yacht was boarded some 200km off the Cork coast in challenging conditions before lunchtime yesterday.
The boarding took place after the Naval Service had been on standby for the yacht’s arrival off the Irish coast since last Sunday.
The intelligence about the vessel came from the Lisbon-based Maritime Analysis Operations Centre-Narcotics (MAOCN).
An armed Navy boarding team from the LE Roisin led the operation with the occupants of the yacht not putting up any resistance when confronted 200km off the Mizen Head.
A second Naval Service vessel, LE Niamh, was in the area for support.
This was in the belief the 55-foot yacht was expected to rendezvous with another craft which would bring the drugs ashore.
The ocean-going yacht was then taken under escort to Cork harbour.
It is expected to berth at Haulbowline Naval Base later tonight where a detailed search operation will be conducted.
Three arrests were made when the yacht was boarded in Irish territorial waters.
The three men will be taken into Garda custody once the yacht is safely berthed at Haubowline.
It is understood all three are UK nationals.
Gardai are liaising with the UK authorities where it is expected that a further four arrests will be made over the next 24 hours.
Irish agencies only boarded the vessel once the UK authorities had been fully briefed.
The yacht was flying an Irish flag when it was boarded but its actual registration remains unclear.
Garda sources stressed that the value of the seizure cannot be confirmed until the yacht is forensically examined and the suspected drug shipment is subjected to a detailed laboratory analysis.
The value of the haul will be determined by the purity of the cocaine involved.
It is understood that at least 40 bales were found in the yacht’s hull.
Armed military police sealed off Haulbowline Naval Base yesterday with all private contractors, including a team working on a construction project, being asked to leave the area temporarily for security reasons.
However, if the seizure does involve €80m of cocaine as suspected, it will rank as one of the largest hauls in Irish history.
It is also likely to prove the biggest offshore cocaine seizure in Europe for 18 months.
The biggest drug seizures in Irish history have all been made off the Cork coast.
The largest seizure remains the €440m of high grade Columbian cocaine seized in Dunlough Bay in west Cork in July 2007.
That smuggling plot was scuppered when the UK gang overloaded a smaller boat used to ferry the drugs ashore and accidentally filled a spare fuel tank with diesel instead of petrol.
The boat capsized in heavy seas and the bulk of the gang members were arrested before they could flee.
A total of 62 bales of Columbian cocaine were left floating in the bay with a purity level of more than 75pc and a street value of €440m.
In November 2008, the yacht ‘Dances With Waves’ was intercepted by the Naval Service, Gardai and Customs almost 100km off the west Cork coast.
It was found to be carrying 1.5 tonne of cocaine destined for the UK market.
That shipment, because its purity was not as high as the Dunlough Bay seizure, was eventually given a street value of €400m.
MAOC-N is an initiative by 7 EU Member Countries: France, Ireland, Italy, Spain, Netherlands, Portugal and the UK, with financial support from the Prevention against Crime Programme of the European Union, European Commission - Directorate - General Home Affairs.
The Centre provides a forum for multi-lateral cooperation to suppress illicit drug trafficking by sea and air.