As the United States, Mexico, and Colombia intensified their war on drugs throughout the late 1990s and the 2000s, the cartels had to reimagine various ways that they could smuggle cocaine into the US. With billions of dollars in annual revenue at stake, no idea for getting drugs into the US buyers was considered too outlandish — Sinaloa cartel leader Chapo Guzman even pioneered the use of cross-border drug catapults.

But the ultimate in high-risk, high-reward smuggling is the "narco submarine," homemade subs that can bring thousands of pounds of product to the US at once.

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. And 30% of the drugs that arrived in the US by sea were conducted via narco submarines. Like narco tanks, narco submarines show how cartels have mastered do-it-yourself engineering. Even so, around one in four of the vessels are interdicted. US authorities have captured narco subs with as much as 7.5 tons of cocaine onboard.