The US Drug Enforcement Administration said it helped Ecuador seize a submarine capable of transporting tons of cocaine.
DEA officials said that the diesel electric-powered submarine was built in a remote jungle and captured near a river close to the Ecuador-Colombia border.
Ecuadorean authorities seized the sub before it could make its maiden voyage.
The sophisticated camouflaged vessel has a conning tower, periscope and air-conditioning system.
It measured about nine feet high from the deck plates to the ceiling and stretched nearly a 100 feet long.
The DEA said it was built for trans-oceanic drug trafficking.
One person was taken into custody. DEA Andean Regional Director Jay Bergman said the sub's nautical and payload capacity is a serious development.
Colombia's drug cartels have been known to use home-built submarines to smuggle large amounts of cocaine past US and Colombian patrol boats to Central America en route to the United States.
Colombian authorities discovered these vessels from time to time in recent years.
In August 2007, US forces intercepted a submarine-like vessel packed with tons of cocaine off the coast of Guatemala.
And in July 2008, Mexico's navy seized a homemade submarine carrying a drug shipment off the Pacific coast.