ALAMEDA (CBS SF) – An Alameda-based Coast Guard cutter has captured a drug-smuggling submarine-like vessel off the coast of Panama, arresting four crewmen aboard and seizing more than 12,800 pounds of cocaine, authorities announced Monday.

The Cutter Bertholf was alerted to the sub by a Customs and Border Protection aircraft flying over the region on March 3rd.

Two two interceptor boats were launched and the semisubmersible (SPSS) was boarded. Inside was stashed more than $203 million worth of cocaine.

“Transnational organized crime groups continue to adjust their tactics to avoid detection indicated by a recent rise in the use of SPSS vessels,” said Vice Adm. Charles Ray, commander, Pacific Area. “Despite these efforts, we will continue to execute an offensive strategy that targets, attacks and disrupts these dangerous criminal networks.”

Since June 2015, the Coast Guard has seized five SPSS vessels.

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According to the Coast Guard, the vessels are constructed for illicit trafficking with a mostly submerged hull; a cockpit and exhaust pipe are visible just above water.

The vessels are extremely difficult to detect and stop because of their low-profile.

“They’ve been using this type of conveyance for a few years now. What we’ve seen in the last couple of years since we’ve concentrated our effort is we’re putting more pressure on them. And so we’ve had better results since 2014 because of the pressure we’ve put on them,” Ray said at a press briefing Monday morning.

The crew of the Coast Guard Cutter Northland seized an SPSS approximately 280 miles southwest of the Mexican-Guatemalan border in January. The suspects in that case scuttled the smuggling vessel as Coast Guardsmen arrived at the scene but were apprehended.

“SPSS interdictions are inherently dangerous, yet we persevere to disrupt the funding sources of illicit organizations causing violence and instability in Central America,” said Capt. Laura Collins, commanding officer of the Cutter Bertholf.

Coast Guardsmen from Bertholf entered the seized vessels numerous times to retrieve the drugs and evidence.