U.S. relies on maritime interdiction operations to counter threat of terrorism

Terrorists have obvious reasons to take their operations out to sea. An attack on an oil tanker, for example, could do vast environmental damage and have a sizable impact on international oil markets. Seaborne shipping may be used to transport missiles and other weapons components not easily sneaked through airports. Currently, the United States does not claim the right to stop any and all ships on the high seas, merely on general suspicion. Since 2004, the United States has encouraged other nations, under the American-led Security Proliferation Initiative (SPI), to sign agreements authorizing American naval patrols to inspect merchant ships flying their flags when there is reason to fear the ships are engaged in illicit activities. While more than half the ships engaged in international commerce are covered by these agreements, many are not. American policy implicitly acknowledges that stopping other ships on the high seas would usually be improper. But special circumstances might justify exceptional measures.