Cartels are using these 'narco-submarines' to move tens of thousands of pounds of drugs at a time

Luis Alberto Cruz Hernandez/APNavy sailors ride atop a 10-meter submarine packed with 5.8 tons of cocaine, as it is being towed into the port of Salina Cruz, Mexico, Friday, July 18, 2008.

Mexican and South American drug cartels and their broader networks are entirely dependent on an ability to get their product onto US soil. And if there's one thing that these organizations are good at, it's changing their operating methods in order to stay one step ahead of the game.

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. 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.

Here are some narco subs that the authorities have captured over the years - evidence of the tenacity and resourcefulness of drug trafficking organizations that have to get their product to the US at any cost.