Columbia subject headings:
Harbors--Security measures--United States.
National security--United States.
Ports of entry--Security measures--United States.
Shipping--Security measures--United States.
United States. Dept. of Homeland Security--Management.
Harvard subject headings:
Harbors--Security measures--United States
National security--United States
Ports of entry--Security measures--United States.
Shipping--Security measures--United States
United States. Department of Homeland Security--Management.
Princeton subject headings:
Harbors--Security measures--United States.
National security--United States.
Ports of entry--Security measures--United States.
Shipping--Security measures--United States.
United States. Department of Homeland Security--Management.