Columbia subject headings:
Harbors--Security measures--United States.
Ports of entry--Security measures--United States.
Shipping--Security measures--United States.
Terrorism--United States--Prevention.
Harvard subject headings:
Harbors--Security measures--United States
Ports of entry--Security measures--United States.
Shipping--Security measures--United States
Terrorism--United States--Prevention
Princeton subject headings:
Harbors--Security measures--United States.
Ports of entry--Security measures--United States.
Shipping--Security measures--United States.
Terrorism--United States--Prevention.