MEXICAN and South American cartels are using custom-built submarines to secretly ship tons of narcotics into the US.

The first incognito vessel was detected in 1993. It was built from wood and fiberglass, but could not fully submerge and only travelled at 10 miles per hour.

7 Navy sailors ride atop a 10-meter submarine packed with 5.8 tons of cocaine, as it's towed into the port of Salina Cruz, Mexico, in July 2008. The vessel was equipped with GPS and a compass. Four Colombian crew members were taken into custody Credit: AP2008

7 A police officer walks through a submarine that was discovered under construction in Facatativa, a rural town just outside of Bogota, in September 2000. Police say it would have been capable of shipping 200 tons of cocaine Credit: AP2000

With billions of dollars in annual revenue at stake, Colombian gangs have since devised specialist machines to smuggle cocaine, heroin, cannabis and methamphetamine to American buyers.

The subs are favoured over speedboats because they are near-impossible for radar, sonar and infrared systems to spot.

Jay Bergman, who heads the Drug Enforcement Administration’s Andean division, told TIME the new subs represent a “quantum-leap in technology”.

He commented: “It’s the difference between building a motor-scooter and building a car.”

Built covertly in the Amazonian jungle, the boats can take between five months to a year to make and cost £1.5million - but this is small fry when the cargo they carry has a street value of hundreds of millions.

Some are only intended for one-time use and are often abandoned at sea.

7 Rubbish litters the interior of a 10-meter submarine packed with 5.8 tons of cocaine at the port of Salina Cruz, Mexico, in July 2008 Credit: AP2008

7 Colombian Navy personnel escort a semi-submarine at the Atrato River in Turbo province, near Medellin in June 2009 Credit: Reuters

The bodies are painted turquoise in a bid to conceal them in the water. The crew can track their movements via a small porthole.

Subs are typically made of fiberglass and powered by a 225-260KW diesel engine.

As the vessel is purpose built to transport illicit cargo, the cabin is tiny. Four men will man the sub, and their quarters will be the size of a double bed.

There are no toilet facilities or kitchen areas meaning the crew must plan supplies in advance. They often survive on crackers, canned beans and milk.

Poor ventilation can see the inside temperature of the sub reach 100 degrees Fahrenheit.

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7 U.S. Navy and Costa Rican Coast Guard officers tie-off a self-propelled semi-submersible that was intercepted carrying around seven tons of cocaine Credit: AP2008

Jay added: “There’s always an armed person on board to keep watch over the crew and the cargo. If anyone starts to panic or mutiny, his orders are to eliminate the troublemaker.”

On board gadgets include radios to speak to gang members on the mainland, GPS tracking and cameras with day and night vision.

Low-profile vessels sit above the water line and can carry 10 tons of drugs (with an estimated street value of £200million), while semi-submersibles go completely under the ocean save for a snorkel-like tube that ensure the crew don’t suffocate.

According to a US Foreign Military Studies Office (FMSO) report on narco submarines citing Drug Enforcement Administration statistics, 80% of drugs smuggled into the US in 2012 came from maritime routes.

7 The bodies are painted turquoise in a bid to conceal them in the water. The crew can track their movements via a small porthole Credit: Getty Images - Getty

And, 30% of the drugs that arrived in the US by sea were conducted via narco submarines.

Drug traffickers have to work out how many drugs they can cram into the vessel so it sits low enough in the water – but they need to be careful it’s not so heavy it will sink.

There could potentially be a dozen subs on the sea floor packed full of cocaine and dead crew members.

In a bid to outsmart the anti-drug enforcement officers, it is believed the cartels are trying to build completely submersible vessels.

7 Colombian Navy soldiers guard a home-made submersible seized with 1.6 tons of cocaine on in November 2008 Credit: AFP - Getty

In 2009 the USA detected as many as 60 narco submarine related events moving 330 metric tons of cocaine per year.

Meanwhile, fans of Netflix's Narcos can now stay in Pablo Escobar’s Mexican mansion that has been transformed into a 35-room, eco-friendly boutique hotel.

And, this is the true story of Narcos’ Cali drug cartel, the multi-billion dollar drug gang which handled 90% of Europe’s cocaine and set death squads on their own people.