A narco-submarine (also called narco-sub, drug sub and Bigfoot submarine) is a type of custom-made ocean-going self-propelled submersible vessel built by drug traffickers to smuggle drugs. They are especially known to be used by Colombian drug cartel members to export cocaine from Colombia to Mexico, which is often then transported overland to the United States.The first known vessels, detected in 1993, were semi-submersibles since they could not dive: most of the craft was submerged with little more than the cockpit and the exhaust gas pipes above the water. Newer narco-submarines are fully submersible, designed specifically to be difficult to detect visually or by radar, sonar and infrared systems. Cargoes carried are typically several tons of cocaine. For example, in 2015 a cargo of over eight tons was found on a semi-submersible which had been tracked by aircraft.