(Newser) – A Coast Guard ship seized a semi-submersible vessel carrying 16,000 pounds of cocaine worth more than $180 million last month in what the Coast Guard is calling the largest drug bust of its kind. Even if they did lose two tons of the drug on the way home. The bust was carried out by the California-based Coast Guard cutter Stratton after a Navy aircraft spotted the suspicious vessel about 200 miles south of Mexico. Coast Guard crew members boarded the sub and arrested four suspected smugglers.

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The Los Angeles Times describes a semi-submersible vessel as a low-tech submarine that travels with only its cockpit and exhaust pipe above water. They are reportedly hard to detect and dangerous to operate. Mashable reports that a quarter of the seized cocaine was lost after the crew of the Stratton left it aboard the semi-submersible for stabilization while towing the vessel to shore. It didn't work: The vessel, and the drugs, sank. Though it gave 4,000 pounds of coke a watery grave, the Stratton has seized more than 33,000 pounds of narcotics since May, says the Coast Guard. (This woman tried to smuggle liquid cocaine in a most unusual way.)

