Columbia subject headings:
Harbors--Security measures--United States.
National security--United States.
Terrorism--United States--Prevention.
United States. Department of Defense--Security measures.
Harvard subject headings:
Harbors--Security measures--United States
National security--United States
Terrorism--United States--Prevention
United States. Department of Defense--Security measures.
Princeton subject headings:
Harbors--Security measures--United States.
National security--United States.
Terrorism--United States--Prevention.
United States. Department of Defense--Security measures.