Columbia subject headings:
Harbors--Security measures--United States.
Marine terminals--Security measures--United States.
National security--United States.
Ports of entry--Security measures--United States.
Shipping--Security measures--United States.
Harvard subject headings:
Princeton subject headings:
Harbors--Security measures--United States.
Marine terminals--Security measures--United States.
National security--United States.
Ports of entry--Security measures--United States.
Shipping--Security measures--United States.