Police have seized a nine-metre (30-foot) narco submarine in southern Spain in what is believed to be the first such vessel built in Europe, Europol said on Monday.
The semi-submersible vessel, which is never fully underwater while being operated, was found inside a warehouse in the port city of Malaga, a Spanish police statement said.
It was in the process of being hand-built. Investigators estimated it was being fitted up to transport up to two tonnes of drugs.
Such semi-submersibles are used by drug traffickers to elude detection by coast guard and other authorities.
In November 2019, Spanish police intercepted what was believed to be the first narco submarine ever captured in Europe, but that was built in Latin America where they are almost commonplace.
The Malaga vessel was discovered as part of a major operation involving police from Colombia, the Netherlands, Portugal, the US and the UK with international activity coordinated by Europe's police agency, Europol.
In total, 52 people were arrested and police searched 47 homes in Barcelona, Malaga and eight other Spanish cities.
As well as the semi-sub, they also uncovered a sophisticated laboratory in the Barcelona area capable of producing 750 kilograms (1,650 pounds) of drugs per month, a 15-metre fibreglass speedboat, 400 kilos of cocaine, 700 kilos of hashish and more than 100,000 euros ($120,000) in cash.
More than 300 officers were involved in the operation which began last year when police discovered a network involved in trafficking large quantities of cocaine, hashish and marijuana.
Run by Spanish, Colombian and Dominican nationals, it was based Catalonia in northeastern Spain, with police in November arresting the network's leader in the coastal town of Tarragona as well as 13 accomplices.
Another branch of the network in Spain's southern Costa del Sol was discovered last month.