A series of 37 smuggling interceptions off Central and South America has yielded what officials are calling “the largest known cocaine offload in Coast Guard history,” with 66,100 lbs. of the drug worth more than $1 billion taken at sea by Coast Guard cutter crews and teams operating off U.S. Navy vessels.

The Coast Guard released a video and new details about the July 18 interdiction of a semisubmersible boat laden with 8.4 tons of cocaine in international waters 200 miles south of Mexico. That incident alone is now being called the single largest seizure in Coast Guard history, worth $250 million in wholesale value to drug traffickers.

It also underscores the evolving maritime capabilities of drug cartels. Under pressure from United States law enforcement, helped by the military and allies coordinated through the U.S. Southern Command, cartels seek better ways to protect drug cargos and evade capture.

The U.S. Department of Homeland Security estimates that 32 percent of maritime cocaine shipments northward from Latin America are moving in semisubmersible vessels. The boats have very low profiles to avoid detection by radar and other sensors, with just a turret-like steering station and air intakes and exhaust above the water.

The July 18 capture was the second semisubmersible caught by the crew of the 418’ cutter Stratton, based at Alameda, Calif. It took the 110-member crew 36 hours to unload the 40-foot smuggling craft, before the boat sank as it was being taken under tow.

The Stratton is a National Security Cutter, with an onboard operations center that links it with other U.S. agencies and partners in allied nations. Those communications and data links came into play with the hunt for the semisubmersible, which was first detected by a Navy maritime surveillance aircraft.

“Semisubmersibles are our ‘white buffalo,’” said Capt. Nathan Moore, Stratton’s commanding officer. “They’re extremely rare, seldom seen, but they exist.”