Airplanes, boats and people have long been used to smuggle drugs, but drug dealers are now using another form of transportation -- submarines.

The subs aren't exactly as high-tech as the ones from "The Hunt for Red October" but Mexican and American authorities say they are effective enough.

The Mexican Navy caught a Colombian drug sub this week -- packed with an estimated 5.8 tonnes of cocaine. That's about a quarter of all the cocaine estimated to enter Canada in a year.

On a tip from the U.S., the Mexicans found the sub 200 kilometers off the coast of Oaxaca, and in a daring raid, soldiers rappelled from helicopters on to the deck of the sub and arrested four smugglers before they could scuttle their vessel.

Mexican Navy officials said they knew of the vessels but had never captured one before. The U.S. caught one last year.

It is believed that Colombian drug cartels have about 40 of the subs.

The custom-built subs do not fully submerge but are so low to the water, less than half a metre, that they avoid radar detection.

This forces anti-drug authorities to use aerial surveillance on the high seas - and there is a lot of sea to cover.

The vessel caught Wednesday was about 10-metres long. Costing about US$1 million, the boats are usually painted to blend in with the color of the water, U.S. Coast Guard Cmdr. Thad Allen told reporters in Washington on Friday.

Canada and the U.S. account for about 50 per cent of cocaine use in the world.

With a report from CTV's Tom Walters and files from The Associated Press