For decades, Colombian drug trafficking organization have pursued their trade with amazingly professional ingenuity, staying a step ahead of authorities by coming up with one innovation after another. When false-paneled pickups and tractor-trailers began drawing suspicion at US checkpoints, the traffickers and their Mexican partners built air-conditioned tunnels under the border. When border agents started rounding up too many human mules, one group of Colombian smugglers surgically implanted heroin into purebred puppies. But the drug runners’ most persistently effective method has also been one of the crudest — semi-submersible vessels that cruise or are towed just below the ocean’s surface and can hold a ton or more of cocaine.