WASHINGTON ( CNN ) -- Sophisticated submarine-like boats are the latest tool drug runners are using to bring cocaine north from Colombia , U.S. officials say . Semi-submersible boats used to smuggle drugs are gaining in quality , the Coast Guard says . Although the vessels were once viewed as a quirky sideshow in the drug war , they are becoming faster , more seaworthy , and capable of carrying bigger loads of drugs than earlier models , according to those charged with catching them . `` They tend to be one of a kind , '' U.S. Coast Guard Commandant Thad Allen said . `` They cost up to a million dollars to produce . Sometimes they are put together in pieces and then reassembled in other locations . They 're very difficult to locate . '' The boats are built in the Colombian jungle . They sail largely beneath the surface of the water but can not submerge completely like a true submarine . But they are the latest escalation of a tactical race between smugglers and the U.S. Coast Guard . In the past three months the Coast Guard has learned of more semi-submersible vessels smuggling drugs than it did in the previous six years , when there were 23 cases , officials said . Watch the Coast Guard chase down a semi-sub » . U.S. Coast Guard intelligence officers predict 85 cases this year and 120 next year . In some instances , the semi-subs are towed behind other vessels and are scuttled if they are detected , Allen said . Authorities are investigating reports that some semi-subs are unmanned and are operated remotely , he said . Diplomatic agreements give the U.S. Coast Guard drug-interdiction jurisdiction in partner countries ' waters . Encounters have become so frequent -- and the dangers of boarding the vessels so pronounced -- that the Coast Guard is pushing for legislation that would make the use of `` unflagged '' semi-submersibles in international waters a crime punishable by up to 20 years in prison , even if authorities ca n't recover drug evidence because the smugglers scuttle the transports . `` There 's really no legitimate use for a vessel like this , '' Allen said . An unflagged vessel is one not registered with a government . Allen believes the semi-subs are a response to the Coast Guard 's tactic of using snipers in helicopters to shoot out engines on smugglers ' speedboats . The submersibles ' engines are beneath water level . `` We 're seeing an evolution in the construction , '' he said . `` Early on we saw fiberglass and now we 're seeing steel . '' Early semi-subs were capable of carrying 4 or 5 metric tons of cargo ; newer ones can carry 12 metric tons , Allen said . Their speed has increased to 12 knots , which is `` a pretty good speed on the ocean . '' Despite the increase in the use of the semi-subs , Drug Enforcement Administration officials say most drugs still are transported by traditional methods -- fishing boats , speedboats and airplanes . But Frankie Shroyer , deputy chief of the DEA 's Office of Enforcement Operations , called the use of semi-subs `` an emerging threat and we are attacking it through our investigations and working with the interagency community . '' The DEA 's main focus , however , `` is to dismantle entire organizations , '' he said . `` So we are looking at the organizations that are building these things . ... These are the same organizations that are using containers , the same organizations that are using airplanes , same organizations using go-fast boats . '' Allen said the Coast Guard , the Department of Defense and others are working on how to board the vessels . `` In many cases , they do n't stop . And it 's difficult to slow them down , '' he said . The Coast Guard says drug runners also are resorting to putting refueling vessels far offshore so drug-carrying boats can avoid coastal areas , and even liquefying cocaine and concealing it in fuel . The semi-subs are `` another adaptation ... that we 're going to have to adapt to ourselves , '' Allen said . Last year , the Coast Guard seized a record 355,000 pounds of cocaine worth an estimated $ 4.7 billion -- a 2 percent increase over 2006 . The Coast Guard 's largest cocaine bust ever came in 2007 -- 42,845 pounds stacked in large bundles on the deck of a freighter off the coast of Panama . E-mail to a friend .
Small boats can travel almost completely underwater , Coast Guard says . Semi - subs carry cargo from Colombia to U.S. million - dollar boats built in jungle , sometimes assembled elsewhere . They ' ve been around awhile , but now more sophisticated , carrying more cargo .