Cruise missiles a threat to homeland, expert says.

• Position: SECURITY BEAT: Homeland Defense Briefs

As if there weren't enough things to worry about, add the possibility of terrorists or a rogue nation launching a cruise missile from a commercial ship at a U.S. city to the list. Ben Stubenberg, chief of analysis and scenarios at the Missile Defense Agency, spends his days imagining such events. He admitted that his theory is an "exotic threat" and "controversial" in Washington. "Not everyone buys into this," he told a Defense News Media Group conference. But the possibility is being discussed more frequently in government defense circles, he said.

In such a plot, a container ship hiding a cruise missile, or perhaps an unmanned aerial vehicle, comes close enough to a major city or port and sends the projectile into the heart of a downtown area.

One example would be a ship heading to the port of Ensenada on the northern section of Mexico's Baha Peninsula. While ships heading for U.S. ports must transmit their intentions to Customs and Border Protection 96 hours in advance, including their manifests and crew lists, vessels sailing to Mexico are not required to do so. A ship...