Terrorists could use drug submarines to smuggle weapons of mass destruction into the the USA. Currently, these submersibles are very popular with drug runners. The Coast Guard encountered 27 of them in the last year. That is six times the previous years rates. These submarines are very difficult for aircraft and surface ships to detect. It is not known how many illegally enter US waters each year. I would guess that several times the number detected and found are missed each year.
The Boston Globe
For US, a terror threat lurks in drug smuggling subs
Shift of cargo to arms and people is feared
By Bryan Bender
KEY WEST, Fla. - Skimming just below the surface, they are extremely difficult to detect from surveillance aircraft or patrol boats. Their sleek design, up to 80 feet in length, can secretly carry several tons of cargo thousands of miles.
These "semi-submersibles," which exhibit some of the same characteristics as military submarines, mark a significant advancement in the ability of drug smugglers to slip past coastal defenses.
So far this year, the Coast Guard says it has encountered at least 27 such vessels headed toward the southern and western United States, more than in the previous six years combined, while far more are believed to have gone undetected, according to US military and law enforcement officials.
The growing number and increased sophistication of the vessels, officially designated "self-propelled semi-submersibles," has set off alarms at the highest levels of the US military and the federal Department of Homeland Security. Counterterrorism officials fear that what drug runners now use to deliver cocaine, terrorists could one day use to sneak personnel or massive weapons into the United States.
Navy Admiral James Stavridis, commander of the US Southern Command, the Miami-based military command that concentrates on Latin America, warned in a recent military journal article, "If drug cartels can ship up to 10 tons of cocaine in a semi-submersible, they can clearly ship or rent space...
Full story here.