The U.S. guards the border. The Mexican army patrols the streets.

Yet the cartels keep coming up with new ways to get their drugs into the United States.

Police in Mexico recently seized a "narco-tank," a pickup truck fitted with steel armor, reports the BBC (see photo).

A drug gang is thought to have transformed the 2011 F-Series Super Duty into a homemade armored vehicle fitted with metal reinforcements.

Here are a few more examples of the creative efforts of Mexico's drug traffickers:

• Smugglers are moving tons of drugs toward the United States in so-called “semi-submersibles,” homemade vessels that travel just below the ocean’s surface and cover distances of up to 2,000 miles. Because they leave tiny wakes, the crude subs are extremely difficult to detect visually or by radar.
• They've also modified an ultralight aircraft with drop baskets that can hold 150 to 250 pounds of marijuana wrapped in brick-sized units and covered in plastic. They move a lever, and the bricks fall to the desert for ground crews to pick up and smuggle onward across the country.
• Police uncovered a 2,200-foot tunnel linking the Mexican city of Tijuana with Otay Mesa in California. The tunnel had a ventilation system, electricity, and a rail system.
• An armored tank, named El Monstruo 2011, had a top speed of 68 mph and could hold up to 12 people — but had no side shielding for its tires, which ultimately led to its capture earlier this month.
• Drug smugglers used a catapult to fire contraband over the border between Mexico and Arizona. Still images taken at the scene shows soldiers testing the catapult, which was powered with elastic and was brought in mounted on a trailer. 

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