Spanish authorities, acting on intelligence from Britain's National Crime Agency (NCA), intercepted a marine support vessel, Thoran, on October 1, in international waters midway between the Azores and Madeira, and discovered four tons of cocaine, worth US$260 million.
The ship was towed to the Spanish port of Cadiz where it arrived on Friday, October 6, and when it was unloaded the total amount of contraband weights 3,700 kilograms.
Seven crewmen, who were from Turkey and Azerbaijan, were arrested and are in custody in Spain awaiting trial.
The drugs, in 165 waterproof packages, had been hidden in a sophisticated compartment under the floor of the ship's kitchen, or galley.
Destined for Europe
The NCA said they could not be sure where the boat was heading, but it was somewhere in Europe and the drugs on board would have been worth £200 million (US$260mln) on the street.
The Thoran, which was flying the flag of the Comoro Islands — a common maritime flag of convenience — had been spotted making an unusual maneuver off the coast of South America.
On September 15, it was spotted off the coast of Suriname, a former Dutch colony, and it is thought that was where the drugs was brought on board.
The interception was a joint operation between the NCA, Spanish Customs, the Spanish National Police and the Guardia Civil, and was coordinated from a control room in Lisbon.
"Seizing this quantity of cocaine represents a major disruption to international crime groups, depriving them of revenue potentially running into the hundreds of millions of pounds," said Mark Blackwell, from the NCA.
"We're working with colleagues in Europe and around the world to disrupt organized criminals in any way we can, and to protect UK and European borders from attempts to smuggle illegal commodities through them," he said.
The NCA was involved in the seizure of 79.3 tons of cocaine in 2016/17.
In May, Spanish authorities tipped off their colleagues in Ecuador, who intercepted a ship carrying 5.5 tons destined for Spain.