U.S. Navy, Customs and Border Protection and Coast Guard personnel took part in the operation last Saturday. The semi-submersible vessel was tracked in international waters off the El Salvador coast by U.S. aircraft. It was intercepted by the Coast Guard after a speedboat began to approach.
Inside the semi-submersible authorities found 274 bales packed with 16,870 pounds of cocaine with an estimated value in the hundreds of millions of dollars. Four suspected smugglers were taken into custody.
Traffickers use submarine-like vessels to move large amounts of cocaine because their low waterline profile makes them difficult to detect.
The interdiction is part of a 15-nation effort targeting international drug traffickers.
Narco subs were first spotted in the 1990s and were designed to sit underwater with only a cockpit and exhaust pipes above the waves.
Since then Colombian police have found true submarines, capable of diving 300 ft, under construction.