Smuggling submarines are like the unicorns of the drug-busting world — or at least they were until the Coast Guard took down five of them in nine months. Or at least they were, until the Coast Guard took down five of them in less than a year.

On March 3, The national security cutter Bertholf made the latest bust, seizing more than 6 tons of cocaine from a self-propelled semi-submersible off the coast of South America on March 3. It was the cutter's second sub bust in a year and the fifth for the service overall.

"It's an indication of the adaptability and the unlimited resources of these organizations that are moving these drugs and have the potential to move anything," Vice Adm. Charles Ray, head of Pacific Area Command, told reporters at a news conference Monday.

Bertholf last tracked down a drug sub in August, just weeks after the cutter Stratton picked up its second unicorn of that patrol. A bust by the cutter Northland in January made four, just as Alameda, California-based Bertholf was heading out for another deployment.

By comparison, the Coast Guard nabbedcaught just one drug sub in 2014 after two years of no busts at all, PACAREA spokesman Lt. Donnie Brzuska told Navy Times.

The increased interdictions are a product of increased drug  production and trafficking activity, Ray said, and but also the Coast Guard's surge of forces to the Eastern Pacific since 2014.

Fiscal 2015 saw 191 tons of cocaine seized and more than 700 smugglers detained, he said, with 100 tons and 270 smugglers racked up so far this fiscal year.

"What we've seen in the past couple of years as we've concentrated our resources is we're putting pressure on them," Ray said.

However, while the Coast Guard estimates they are able to get intelligence on 90 percent of drugs coming through the Pacific from South America, they are only able to interdict two in 10 of these vessels20 percent of that, he said.

"We've increased our intelligence capabilities and we understand the organizations better than we did just a few years ago," he added, but with resources stretched thin, they have to make decisions about which pursuits will come with the biggest hauls.

Drug kingpins pay builders to fabricate Those organizations are paying builders to construct these narco subs in the jungles of South America, out of wood, aluminum or steel and fiber glass, which can be loaded down with bales of cocaine and a few men to operate. These subs typically skirt along the coasts of South America and Central America, steaming near the surface with little of the sub's frame peeking out of the water to maximize their chances of being discovered by radar or aircraft. The drugs are often offloaded on Mexico's southern coast and then driven into the U.S., Brzuska said.and navigate the boat as peeks slightly out of the open water. 

In general, they head from the coast of South America up to Central America or the southern coast of Mexico, where the drugs are driven across the border to America, Brzuska said.

"It's pretty amazing — they have access to the same type of off-the-shelf GPS products that if you had a boat in Alameda and you were to sail down to San Diego," Ray said.

Catching them is a widely concerted effort. In the most recent bust, a U.S. Customs and Border Protection aircraft spotted the sub March 1, according to Bertholf skipper Capt. Laura Collins, calling on her ship to chase go after it just northwest of the Galapagos Islands.

The cutter launched two small boat teams and a helicopter March 3. Video of the bust shows the first boat team boarding the sub at gunpoint, then a second boat coming alongside while the sub's crew stood on top with their hands raised.

It's a dangerous operation from start to finish, Collins said, even if the crew surrenders. Once inside, the boarding team found a loaded gun in the cockpit, according to a Coast Guard release.

"Semi-submersibles are extremely un-seaworthy," she said. "We treat each one as if it were a sinking vessel until we can complete our own safety evaluation."

With no way to tow the sub back to shore and no good way to get local law enforcement to come out and get it, the crew decided to weigh down and sink itthe sub. The whole operation took from 10 to 12 hours, Collins said.