Spanish authorities have captured what is believed to be the first-ever narco submarine to cross the Atlantic Ocean.

Law enforcement estimate they have confiscated three tons of cocaine worth upwards of $121 million from the 65-foot vessel, which was intercepted Sunday in the northwestern region of Galicia, Spain.

Two Ecuadorian members of the three-person crew were arrested by police after they scuttled the vessel. The third man, who is Spanish, is currently on the run.

The submarine was tracked while it sailed across the Atlantic from Colombia to Europe - a journey of 7,690 kilometres or 4,778 nautical miles.

The sophistication of the 65-foot vessel has caught authorities off-guard as South American drug cartels employ increasingly brazen methods of delivering their merchandise across the globe. 

Sources close to the investigation said the groups behind this shipment must be 'big' since the submarine itself must have cost around $2.7 million.'

Spanish authorities said it was the first time a submarine had been found to be used in drug trafficking in the country. Police divers pulled out one package of cocaine from the vessel Monday. (Daily Mail)