Today, smugglers are moving tons of drugs towards the United States in so-called semi-submersibles, homemade vessels that travel just below the oceans 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. Even when they are spotted, crew members quickly sink the vessels to get rid of the evidence and avoid being prosecuted for drug trafficking.

Authorities seized 14 semi-submersibles last year, and another six have been captured this year, according to Col****ian Navy Capt. Mario Rodriguez.

Most of the vessels move between Col****ia and drop-off points in Mexico and Central America. But in 2006, police discovered a scuttled 33-foot-long semi-submersible off the northwest coast of Spain.

Col****ian authorities now believe that up to 70 percent of the cocaine leaving the countrys Pacific coast is packed aboard semi-submersibles. U.S. Sen. Frank Lautenberg, a New Jersey Democrat, estimated that the vessels this year would ship up to 480 metric tons of cocaine.

They went from being an urban legend to some sporadic seizures to a flurry in the last two years, said an official at the U.S. embassy in Bogota. Semi-submersibles are the transportation of choice for maritime drug traffickers.

The smugglers are trading speed for stealth.

They used to prefer go-fast boats, high-speed fiberglass watercraft that can carry 2 tons of drugs and travel up to 80 miles per hour in calm seas. But those crafts leave huge wakes and anti-drug agents, using helicopters and their own racing boats, have become far more adept at spotting them.

So, the traffickers have moved underwater by making modifications to the go-fast boat design. A semi-submersible is, in essence, a go-fast boat with a fiberglass top fitted with air vents that stick out of the water.

Instead of high-speed engines, the semi-submersible is powered by a 200 or 300 horsepower diesel motor, allowing the vessel to move about 10 miles per hour. The resulting wake is so small that anti-drug agents or Coast Guard officials must get within 3,000 yards of the vessels to spot them.

Most semi-submersibles are built along the rivers, estuaries and mangrove swamps of Col****ias Pacific coast, at a cost of between $500,000 and $1 million per vessel.