Terrorism experts fear that the world's oil tankers, sea lanes and major ports are dangerously vulnerable to 9/11-scale attacks that would cripple world trade. They cite an alarming combination of factors, including terrorist-connected Southeast Asian rebels involved in piracy, the difficulty of tracking suspect vessels in the murky world of commercial shipping, and an Al Qaeda fleet that could be as large as 300 vessels. Plots that have already been carried out include the October 2000 attack on the U.S. destroyer Cole in the port of Aden in Yemen, which killed 17 sailors, and the attack last October on the...