America's ports are a vital part of the nation's economy. Since the September 11, 2001 terrorist attacks, protecting the country's ports and waterways has been a critical component of guarding against future terrorist attacks. VOA's Chris Simkins reports on how U.S. Customs agents are protecting the major western U.S. port of Seattle, Washington.

More than a million shipping containers from all parts of the world arrive here every year. The Seattle Area port system is one of the largest in the United States.

Since the 9-11 terrorist attacks security has been significantly heightened, including inspections of overseas shipping containers. The process starts at the U.S. Customs targeting unit.

Agent James Sullivan says he and other inspectors track foreign cargo manifests before a ship is even loaded overseas. "We screen those shipments for a variety of purposes for everything from counter-terrorism, commercial fraud, narcotics violations.

After the screening is completed we decide which cargo containers to put on hold and then we place those containers on hold and send them for an examination."

Customs agents can also use X-ray machines mounted on trucks called VACAS to look for suspicious cargo after they are unloaded from the ship.

They can even remove material from containers for closer physical inspections, using trained dogs to sniff out illegal items such as drugs.

But what concerns security experts the most is that terrorists might smuggle a small nuclear bomb or materials used to make a so-called dirty bomb in one of the thousands of shipping containers that come into Seattle every day.

Now ports, like Seattle, Oakland and San Francisco, cargo containers pass through new radiation detection devices, says John Barnes, of the U.S. Customs and Border Protection. "Radiation Portal monitors are specifically designed to detect all types of radiation -- those radiation that might be used to make dirty bombs."

Agent Barnes says the ultimate goal is to have 100 percent of all cargo pass through the new radiation portal monitors. Some of the nation's 300 other ports will have similar devices in the future.

Mr. Barnes says the new technology will help protect U.S. ports while maintaining the free flow of goods. "We have the daunting task of ensuring the public safety in the United States and we take that very seriously, but as well we also are interested in keeping the free flow of the economy going here in the United States."

James Carafano, a security analyst with the Heritage Foundation in Washington DC, says early warning systems are some of the best ways to stop terrorism at American seaports.

"I think the approach we have here is really right. What we want to do is inspect 100 percent of the high-risk cargo. In other words, 100 percent of the cargo in which there is an anomaly, that there is something suspicious about, that we should look at. That again is a question of the right intelligence, the right information, the right counter-terrorism, to identify what does not fit the pattern."

The Department of Homeland Security says it will spend millions of dollars over the next few years to better enhance security at all ports, knowing that, otherwise, maritime transportation systems including ports are attractive targets for terrorists.