Prevention Security measures Terrorism -- 8 Merchant marine -- 3 National security -- 3 Aeronautics, Commercial -- 2 Airports -- 2 more ... Hijacking of aircraft -- 2 Safety measures 2 Security measures -- 2 Transportation -- 2 Boats and boating -- 1 Civil defense 1 Civil defense -- 1 Defenses 1 Freight and freightage -- 1 Harbors -- 1 Hijacking of ships -- 1 Homeland security 1 Infrastructure -- 1 Military policy 1 National security 1 Passenger traffic 1 Pirates 1 Politics and government -- 1 Security Management 1 Shipping -- 1 Surface-to-air missiles 1 Total quality management 1 United States 1 less ...