The U.S. Navy has a major headache in trying to deal with the threat of terrorist attack using merchant ships. There are some 121,000 merchant ships in service, of which 89,000 are a hundred tons or larger. About 70 percent of them are at sea at any given time. Fortunately, only 350-400 arrive at American ports each day, mainly because to save money, only the largest cargo or tanker ships are used to move stuff in or out of the United States. These large ships are very expensive, and operated by reputable firms who see to it that things are run efficiently by professional officers and sailors. Its the more abundant smaller ships that are more worrisome. Except for some long range fishing boats and pleasure craft, few of the smaller merchant ships should be crossing the ocean to reach North America. Many of those that do are found to be involved in smuggling (most often people or drugs). 

The Coast Guard is overwhelmed just trying to increase security at the major ports, so the navy is doing more at what was always a navy chore; oceanic surveillance. During the Cold War, this meant keeping an eye on the Russian fleet. But the Russian warships are largely gone, and now there are hundreds of smaller merchant vessels on the high seas, approaching Americas coasts. Many of these are innocent, but some are up to no good. The navy is trying to set up a system that will track suspicious ships. Maritime patrol aircraft, space satellites and, increasingly, UAVs, are being used. 

In the Pacific ocean, where the greatest terrorist threat exists, the U.S. Navy has established the "Regional Maritime Security Initiative." This program integrates the naval intelligence efforts of many different nations so that there is a better chance to catch seagoing terrorist operations. Many Pacific nations are concerned with local piracy and smuggling problems, so it is to their advantage to gain access to information from the American navys more extensive surveillance system. Pacific nations that host a lot of seagoing traffic are aware that they could be the victims of a terrorist plot to seize a ship with an explosive target, take it to a nearby port, and detonate it. 

The U.S. navy also has to supply ships that can intercept suspicious ships that illegally enter American waters. At the moment, a lot of the potentially suspicious traffic goes along without getting much attention. The extent of the problem is kept secret, so as not to provide useful information for any potential terrorists. But the vulnerability is real, and may not be taken care of for some time. Meanwhile, much public attention is paid to a more visible threat, the millions of cargo containers that large cargo ships bring into American ports each year. Ports in California alone handle over eight million containers a year. But scrutinizing these may prove easier to handle than all those smaller ships lurking off our coasts.