Cocaine worth more than £500 million – one of Europe’s largest hauls – has been seized off the southwest coast of the Irish Republic in an operation that is thought to have targeted a British criminal gang.

A 60ft yacht once registered as British was being examined yesterday and three men – two of whom were described by Irish police as English and aged between 44 and 52 – were under arrest after the international operation. The third man was believed to be from Dublin.

Police, naval and Customs services all took part in the arrest of the yacht, Dancing With Waves, which was escorted into Castletownbere harbour, West Cork. The vessel had been tracked for a month from the Caribbean.

The yacht was carrying 75 bales of cocaine, with a high level of purity. The seizure dwarfs that of last year, also in West Cork, when the bungling crew of another yacht ended up in the sea, surrounded by their illegal cargo, after putting the wrong fuel in their inflatable launch’s motor engine.

The Irish Republic is becoming a favourite dropping-off point on international drug-smuggling routes from South and Central America and West Africa. Its rugged southern coast provides many unguarded inlets – ideal as a transit point to move the cargo on to Britain and mainland Europe.

Local fishermen said they were not surprised by the haul. One, Sean O’Driscoll, said that suspicious activity was regularly seen at sea. His trawler had twice snagged bales of cocaine that had been lying on the seabed.

Dancing With Waves was detained late on Wednesday night. The seizure was the result of a European task force codenamed Operation Seabight, involving officers from several nations. The operation was controlled from the Maritime Analysis and Operations Centre in Lisbon, Portugal.

Specially trained armed naval officers boarded the yacht in what an Irish Defence Forces’ spokesman described as a “compliant armed boarding”.

Lieutenant General Dermott Earley, the Irish Defence Forces Chief of Staff, paid tribute to the crew of the Irish Navy vessel LE Niamh for intercepting the yacht. He said: “The men and women of LE Niamh played a crucial role in the apprehension of these personnel. Armed boarding parties travelling in rigid inflatables from the ship boarded the yacht at night, some 150 nautical miles from the coast and arrested three men.

“I know in the coming weeks and months a lot of long hours of investigation will be undertaken by, in particular, An Garda Siochana [the Irish police]. However, the Naval Service will continue to work very closely with them and give every assistance available.”

General Earley said that the Irish Naval Service operated “in the harshest of conditions off the coast of Ireland” and would continue their work hunting down drug traffickers.

“The sharp end of this operation will grab headlines. However, it is also an occasion to point to the excellent cooperation at Joint Task Force level between the Naval Service, An Garda Siochana and the Customs Service.”

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