According to CNN International:
A drug-trafficking organization built the sea-worthy vessel that is now being held near the border of Ecuador and Colombia, and one individual has been taken into custody, authorities said. "This is the first seizure of a clandestinely constructed fully operational submarine built to facilitate trans-oceanic drug trafficking," the Drug Enforcement Administration said in a statement.
The vessel utilized twin screws and was diesel electric-powered, the agency said. It was about 30 meters (98 feet) long and nearly 3 meters (nine feet) high from the deck plates to the ceiling. It has a periscope and an air-conditioning system.