The vessel, which is nine meters long, three meters wide and three meters deep (30 x 10 x 10 feet), was found in a warehouse in Malaga, southern Spain, according to a press release from Spain's national police published Friday. It was discovered during an operation against a sophisticated drug smuggling ring that resulted in 52 arrests, the force said.
Semi-submersibles are hard to detect but expensive to build. They have long been used by drug traffickers working in Latin America but are thought to be much less common in Europe.
In November 2019, a 22-meter (72-feet) vessel carrying 3,000 kilograms (6,614 pounds) of cocaine and thought to have originated in Colombia was seized off the coast of Galicia in Spain. However, this is the first time a Spanish-made craft has been discovered by police.
It consists of a plywood and fiber glass frame built around an existing keel, and boasts two 200 horsepower outboard motors operated using a control panel inside the cockpit, according to police.
Rafael Pérez, commissioner of Spain's judicial police, said that construction was ongoing when the vessel was seized and it had never been tested in the water.
Speaking at a press conference, Peréz said he believed the vessel would have been used to sail to meet a drug-carrying mothership out at sea.
The semi-submersible was found during a long-term investigation involving cooperation with security forces in Colombia, the Netherlands, the UK, the US and Portugal, according to the press release.
More than 300 Spanish police carried out 47 searches along the country's Mediterranean coast.
Investigators discovered a number of properties linked to drug trafficking, including a "sophisticated clandestine laboratory" in the Barcelona region with the capacity to extract and process up to 750 kilograms (1,653 pounds) of cocaine per month, as well as 12,000 liters of precursor chemicals.
In February, police arrested one of the principal suspects at El Prat airport in Barcelona as he was about to get on a flight to the Netherlands.
Thirty of those arrested are currently in custody awaiting trial.
During the investigation, Spanish police also seized a 15-meter fiberglass boat, 400 kilograms (882 pounds) of cocaine, 700 kilograms (1,543 pounds) of hashish and more than 100,000 euros ($119,280) in cash.
In January, Spanish police seized more than two tons of cocaine and arrested 12 people allegedly involved in a large scale drugs smuggling network with connections to Paraguay and Brazil.
Authorities investigated the network -- members of which had attempted to cover their tracks by setting up legitimate businesses -- for more than a year, according to a statement from Spain's national police.